💀 Blue Screen Error (BSOD)

Fix Repair 0xC000021A Windows 10 Blue Screen Error - Complete Solution Guide

📅 Updated: Jan 14, 2026 ⏱️ 30-90 min read ✅ Verified Solutions

🚀 Quick Fix Summary

Error Type: Blue Screen of Death (BSOD) - Critical System Error

Error Code: 0xC000021A

Common Causes: Winlogon.exe or Csrss.exe failure, corrupted system files, incompatible drivers, failed Windows updates, third-party software conflicts

Time to Fix: 30-90 minutes

Difficulty: Advanced

Success Rate: 85% with proper method selection

The "Blue Screen of Death (BSOD) Error 0xC000021A" is a critical Windows system error that occurs when essential system processes (Winlogon.exe or Csrss.exe) fail to start or terminate unexpectedly, preventing Windows from loading properly. This error is one of the most serious Windows errors because it indicates that core system components required for Windows to function have failed, typically resulting in a blue screen with the error message "STOP: c000021a {Fatal System Error} The session manager initialization system process terminated unexpectedly with a status of 0xc000021a" and forcing the system to shut down or restart in a continuous loop.

Error 0xC000021A specifically indicates that either Winlogon.exe (Windows Logon Process) or Csrss.exe (Client/Server Runtime Subsystem) - two critical system processes that must run for Windows to function - have failed during system startup or runtime. These processes are responsible for user authentication, session management, console windows, and critical system operations. When either process fails, Windows cannot continue operating and must shut down to prevent data corruption or system instability.

This error is particularly severe because it prevents normal Windows boot, often trapping users in a boot loop where the system attempts to start, encounters the error, displays the blue screen, and restarts repeatedly. The error affects Windows 10, Windows 11, Windows 8.1, Windows 7, and Windows Server editions. Common scenarios include systems that fail to boot after Windows updates, systems with corrupted system files, systems with incompatible or corrupted drivers, systems where third-party security software or system utilities have modified critical system files, and systems that have experienced improper shutdowns or power failures during critical operations.

Understanding that 0xC000021A requires immediate attention and often advanced troubleshooting is crucial. Unlike many errors that allow Windows to boot, this error typically prevents normal system startup, requiring boot from Windows installation media, Safe Mode access, or Advanced Startup Options. This comprehensive guide provides five proven methods to resolve Error 0xC000021A, including system file repair using DISM and SFC, booting into Safe Mode for troubleshooting, using System Restore to revert to a working state, performing a clean boot to identify conflicting software, and using Windows installation media for advanced repair options.

Understanding Blue Screen Error 0xC000021A

Error 0xC000021A is a fatal system error that occurs when critical Windows processes (Winlogon.exe or Csrss.exe) fail. These processes are essential for Windows operation - Winlogon handles user logon and authentication, while Csrss manages console windows and critical system functions. When either process fails, Windows cannot continue and must shut down.

Where this error typically occurs:

  • System startup - during Windows boot process
  • After Windows updates - when updates corrupt system files
  • During system operations - when critical processes crash
  • After driver installations - when incompatible drivers are installed
  • After software installations - when software modifies system files incorrectly

Common error messages you might encounter:

  • "STOP: c000021a {Fatal System Error} The session manager initialization system process terminated unexpectedly"
  • "Error 0xC000021A - Fatal System Error"
  • "Your PC ran into a problem and needs to restart. We're just collecting some error info"
  • Blue screen with 0xC000021A error code
  • System stuck in boot loop

Why Error 0xC000021A occurs:

  • Corrupted system files: Winlogon.exe, Csrss.exe, or related system files are damaged or missing
  • Failed Windows updates: Incomplete or corrupted Windows updates modify critical system files incorrectly
  • Incompatible drivers: Corrupted or incompatible device drivers cause system process failures
  • Third-party software conflicts: Security software, system utilities, or other software modify system files incorrectly
  • Registry corruption: Corrupted Windows registry entries prevent system processes from starting
  • Hardware issues: Failing RAM, storage drive errors, or other hardware problems cause system instability
  • Malware infection: Malware corrupts or replaces critical system files

Method 1: Repair System Files Using DISM and SFC (From Windows Installation Media)

This method repairs corrupted system files that cause Winlogon.exe or Csrss.exe to fail. Since 0xC000021A often prevents normal boot, we'll use Windows installation media to access Command Prompt.

Repairing system files using DISM and SFC to fix 0xC000021A error
  1. Boot from Windows installation media:
    • Insert Windows 10/11 installation USB or DVD
    • Restart computer and boot from installation media
    • Press any key when prompted "Press any key to boot from CD or DVD"
    • Wait for Windows Setup to load
  2. Access Command Prompt from installation media:
    • On Windows Setup screen, click Next
    • Click Repair your computer (bottom left)
    • Select Troubleshoot → Advanced options → Command Prompt
    • Command Prompt will open
  3. Identify Windows installation drive:
    • In Command Prompt, type: dir C:\Windows and press Enter
    • If Windows folder appears, C: is your Windows drive
    • If not, try D:, E:, or other drives until you find Windows folder
    • Note the drive letter (we'll use C: in examples, replace if different)
  4. Run DISM to repair component store:
    • Type: DISM /Image:C:\ /Cleanup-Image /RestoreHealth
    • Press Enter - this repairs Windows component store
    • Process takes 15-30 minutes - do not interrupt
    • Wait for "The operation completed successfully" message
  5. Run System File Checker:
    • Type: sfc /scannow /offbootdir=C:\ /offwindir=C:\Windows
    • Press Enter - this scans and repairs system files
    • Process takes 20-60 minutes - do not interrupt
    • Wait for scan to complete
  6. Check repair results:
    • Review DISM and SFC output messages
    • Look for "Windows Resource Protection found corrupt files and successfully repaired them"
    • If errors persist, note the specific error messages
  7. Exit Command Prompt and restart:
    • Type: exit and press Enter
    • Remove installation media
    • Restart computer normally
    • Check if 0xC000021A error is resolved

Why this works: Error 0xC000021A is often caused by corrupted Winlogon.exe, Csrss.exe, or related system files. DISM repairs the Windows component store (source of system files), and SFC uses the repaired store to fix corrupted system files. This restores critical system processes to working condition.

Method 2: Boot into Safe Mode and Use System Restore

If you can access Safe Mode, System Restore can revert your system to a point before 0xC000021A appeared, restoring working system files and configurations.

Booting into Safe Mode to fix 0xC000021A error
  1. Access Advanced Startup Options:
    • If system is in boot loop, force shutdown (hold power button 10 seconds)
    • Start computer - when Windows logo appears, force shutdown again
    • Repeat 2-3 times until "Preparing Automatic Repair" appears
    • Or boot from Windows installation media → Repair your computer
  2. Access Advanced Options:
    • On Automatic Repair screen, click Advanced options
    • Or from installation media: Troubleshoot → Advanced options
  3. Boot into Safe Mode:
    • Select Startup Settings → Restart
    • After restart, press F4 for Enable Safe Mode
    • Or press F5 for Enable Safe Mode with Networking
    • Wait for Windows to boot into Safe Mode
  4. Open System Restore:
    • In Safe Mode, press Windows + R
    • Type: rstrui.exe and press Enter
    • Or search "System Restore" in Start menu
    • System Restore window will open
  5. Select restore point:
    • Click Next on System Restore welcome screen
    • Select a restore point from before 0xC000021A appeared
    • Click Scan for affected programs to see what will be restored
    • Review the list - programs installed after restore point will be removed
    • Click Next → Finish → confirm restore
  6. Wait for System Restore to complete:
    • System will restart and restore to selected point
    • Process takes 15-30 minutes - do not interrupt
    • Computer will restart automatically when complete
  7. Verify system boots normally:
    • After restore, system should boot normally
    • Check if 0xC000021A error is resolved
    • If error persists, proceed to Method 3

When to use this method: Use Method 2 when you have recent system restore points and can access Safe Mode. System Restore is effective if 0xC000021A appeared after a recent change (update, driver installation, software installation).

Method 3: Perform Clean Boot to Identify Conflicting Software

If you can boot into Safe Mode, performing a clean boot helps identify third-party software or services causing 0xC000021A by disabling non-essential startup programs and services.

Performing clean boot to fix 0xC000021A error
  1. Boot into Safe Mode:
    • Use Method 2 steps to boot into Safe Mode
    • Or if system boots normally sometimes, press Windows + R, type msconfig, press Enter
  2. Open System Configuration:
    • In Safe Mode or normal mode, press Windows + R
    • Type: msconfig and press Enter
    • System Configuration window will open
  3. Disable all startup programs:
    • Click Startup tab
    • Click Open Task Manager
    • In Task Manager, disable all startup items (right-click → Disable)
    • Close Task Manager
  4. Disable non-essential services:
    • In System Configuration, click Services tab
    • Check Hide all Microsoft services (important!)
    • Click Disable all to disable all third-party services
    • Click Apply → OK
  5. Restart computer:
    • Click Restart when prompted
    • System will boot with minimal services and programs
    • Check if 0xC000021A error still occurs
  6. If error is resolved, identify conflicting software:
    • If system boots normally, a third-party program/service is causing the issue
    • Re-enable services and programs one by one
    • Restart after each re-enable to identify the culprit
    • When error returns, you've found the conflicting software
    • Uninstall or update the conflicting software
  7. Re-enable essential services:
    • After identifying and removing conflicting software
    • Open System Configuration again
    • Select Normal startup on General tab
    • Click OK → Restart

Why this works: Third-party software, especially security software, system utilities, or drivers, can modify system files or conflict with Winlogon.exe/Csrss.exe, causing 0xC000021A. Clean boot isolates the problem by running only essential Windows services, allowing you to identify the conflicting software.

Method 4: Repair Windows Boot Configuration and Registry

Corrupted boot configuration or registry entries can prevent Winlogon.exe or Csrss.exe from starting properly. This method repairs boot configuration and critical registry entries.

Repairing Windows boot configuration to fix 0xC000021A error
  1. Boot from Windows installation media:
    • Insert Windows installation USB/DVD
    • Boot from installation media
    • Click Repair your computer → Troubleshoot → Advanced options → Command Prompt
  2. Identify Windows drive:
    • Type: dir C:\Windows and press Enter
    • If Windows folder appears, C: is your drive
    • If not, try other drive letters (D:, E:, etc.)
    • Note the drive letter (using C: in examples)
  3. Repair Boot Configuration Data (BCD):
    • Type: bootrec /fixmbr and press Enter
    • Type: bootrec /fixboot and press Enter
    • Type: bootrec /rebuildbcd and press Enter
    • If prompted to add installation to boot list, type Y and press Enter
    • Wait for each command to complete
  4. Repair Windows Registry (Advanced):
    • Type: cd C:\Windows\System32\config and press Enter
    • Type: ren SYSTEM SYSTEM.old and press Enter
    • Type: ren SOFTWARE SOFTWARE.old and press Enter
    • Type: copy C:\Windows\System32\config\RegBack\SYSTEM C:\Windows\System32\config\ and press Enter
    • Type: copy C:\Windows\System32\config\RegBack\SOFTWARE C:\Windows\System32\config\ and press Enter
    • Warning: This restores registry from backup - recent changes will be lost
  5. Run DISM and SFC again:
    • Type: DISM /Image:C:\ /Cleanup-Image /RestoreHealth and press Enter
    • After DISM completes, type: sfc /scannow /offbootdir=C:\ /offwindir=C:\Windows
    • Wait for both to complete
  6. Exit and restart:
    • Type: exit and press Enter
    • Remove installation media
    • Restart computer normally
    • Check if 0xC000021A error is resolved

Warning: Registry repair (step 4) restores registry from backup, which may remove recent software installations or settings. Only use this if other methods fail and you have backups of important data.

Method 5: Reset Windows or Perform Clean Installation (Last Resort)

If all previous methods fail, Windows Reset (keeping files) or clean installation can resolve 0xC000021A by providing a fresh Windows installation. This is the most drastic solution but highly effective.

Resetting Windows to fix 0xC000021A error
  1. Access Windows Reset options:
    • Boot from Windows installation media
    • Click Repair your computer → Troubleshoot
    • Select Reset this PC
    • Or if system boots sometimes: Settings → Update & Security → Recovery → Reset this PC
  2. Choose reset option:
    • Select Keep my files (removes apps but keeps personal files)
    • Or select Remove everything (full reset - backup files first!)
    • Keep my files is recommended to preserve data
  3. Choose installation source:
    • Select Cloud download (downloads fresh Windows) or Local reinstall (uses existing files)
    • Cloud download is recommended for best results
  4. Review what will be removed:
    • Windows will show list of apps that will be removed
    • Review the list - you'll need to reinstall these apps
    • Personal files (documents, pictures, etc.) will be preserved if you chose "Keep my files"
  5. Start reset process:
    • Click Reset to begin
    • Process takes 1-3 hours - do not interrupt
    • Computer will restart multiple times during process
    • Wait for process to complete
  6. Complete Windows setup:
    • After reset, Windows will guide you through initial setup
    • Create user account, configure settings
    • Windows should now boot without 0xC000021A error
  7. Reinstall applications:
    • Reinstall applications that were removed
    • Update Windows immediately
    • Install antivirus and security software
    • Restore files from backup if needed

Warning: Windows Reset removes all installed applications. "Keep my files" preserves personal files but removes apps. "Remove everything" deletes everything. Always backup important data before resetting. Use Method 5 only when Methods 1-4 fail, as it requires significant time and reconfiguration.

💡 Pro Tip: Prevent 0xC000021A Errors

Keep Windows and drivers updated: Regular updates include fixes for system file corruption and driver compatibility issues that can cause 0xC000021A. Use reputable software: Only install software from trusted sources. Malware and poorly coded software can corrupt system files. Create regular system restore points: Before major updates or software installations, create restore points for easy rollback. Avoid interrupting Windows updates: Let Windows updates complete fully - interruptions can corrupt system files. Monitor system health: Run SFC and DISM scans monthly to catch file corruption early before it causes critical errors like 0xC000021A.

Additional Troubleshooting Steps

Check Hardware Health

Hardware issues (failing RAM, storage drive errors) can cause 0xC000021A. Run memory diagnostics: Press Windows + R, type mdsched.exe, press Enter, choose to restart and check for memory problems. Check storage drive health using manufacturer's diagnostic tools.

Check Windows Event Viewer (If Accessible)

If you can boot into Safe Mode, check Event Viewer for detailed error information: Open Event Viewer → Windows Logs → System. Look for error entries around the time 0xC000021A appeared. Event Viewer often provides more specific information about which process failed and why.

Update BIOS/UEFI

Outdated BIOS/UEFI firmware can cause system instability leading to 0xC000021A. Visit your motherboard manufacturer's website, download latest BIOS update, and update BIOS following manufacturer's instructions. Warning: Incorrect BIOS update can damage your system - only update if you're experienced or have professional help.

Prevention Strategies

  • Keep Windows updated: Regular updates include system file fixes and security patches
  • Use reputable software: Only install software from trusted sources to avoid malware
  • Create system restore points: Before major changes, create restore points for easy rollback
  • Don't interrupt Windows updates: Let updates complete fully to prevent file corruption
  • Regular system maintenance: Run SFC and DISM scans monthly to catch corruption early
  • Keep drivers updated: Update device drivers regularly to prevent compatibility issues
  • Monitor system health: Use Windows built-in tools to monitor system stability

When to Seek Professional Help

If all methods fail to resolve 0xC000021A, consider these scenarios:

  • Hardware failure: If hardware diagnostics reveal failing components, hardware replacement may be necessary
  • Persistent file corruption: If system files cannot be repaired, professional data recovery and system repair may be needed
  • Critical data at risk: If you cannot afford data loss, professional services can recover data before system repair
  • Enterprise environments: In business environments, consult IT support before attempting advanced repairs

Frequently Asked Questions

Q: Can I fix 0xC000021A without losing my files?

A: Yes, Methods 1-4 preserve your files. Method 5 (Windows Reset) with "Keep my files" option also preserves personal files but removes installed applications. Always backup important data before attempting repairs, as advanced troubleshooting can sometimes result in data loss.

Q: Why does 0xC000021A keep appearing after I fix it?

A: Recurring 0xC000021A indicates underlying issues like failing hardware (RAM, storage drive), persistent malware, or incompatible software that keeps corrupting system files. Run hardware diagnostics, perform thorough malware scan, and identify conflicting software using clean boot (Method 3).

Q: Is 0xC000021A caused by a virus or malware?

A: Sometimes, yes. Malware can corrupt or replace critical system files like Winlogon.exe or Csrss.exe, causing 0xC000021A. However, the error is more commonly caused by corrupted system files, failed updates, or incompatible drivers. If you suspect malware, boot into Safe Mode and run a full antivirus scan.

Q: Can I prevent 0xC000021A from happening?

A: While you cannot completely prevent it, you can significantly reduce risk by: keeping Windows and drivers updated, using reputable software, creating regular system restore points, not interrupting Windows updates, running regular SFC/DISM scans, and monitoring system health. These practices help prevent the file corruption and conflicts that cause 0xC000021A.

Q: How long does it take to fix 0xC000021A?

A: Method 1 (DISM/SFC) takes 30-60 minutes. Method 2 (System Restore) takes 15-30 minutes. Method 3 (Clean Boot) takes 20-40 minutes plus time to identify conflicting software. Method 4 (Boot/Registry repair) takes 30-60 minutes. Method 5 (Windows Reset) takes 1-3 hours. Total time depends on which method successfully resolves your specific case and system speed.