The Windows stop code 0xC000021A is a critical Blue Screen of Death (BSOD) error that occurs when a crucial system process, typically winlogon.exe or csrss.exe, encounters an unrecoverable issue. This error prevents your Windows 11 or Windows 10 system from booting properly, leaving your computer stuck in a restart loop or a blue screen.

Common triggers for this error include corrupted system files, recent system updates, incompatible device drivers, or hardware issues. Below are several methods you can use to diagnose and resolve the 0xC000021A error effectively.

Method 1: Boot into Safe Mode to Troubleshoot

Step 1: To enter Safe Mode, first force your computer to restart three times by pressing and holding the power button each time Windows begins loading. After the third attempt, Windows will automatically enter Automatic Repair mode.

Step 2: In the Automatic Repair screen, select Troubleshoot > Advanced options > Startup Settings. Click Restart.

Step 3: After the system restarts, press F4 to boot into Safe Mode or F5 to boot into Safe Mode with Networking.

Once in Safe Mode, you can perform troubleshooting steps such as uninstalling recent updates, removing problematic software, or updating device drivers.

Method 2: Run Startup Repair

Step 1: Boot your system into the Windows Recovery Environment (WinRE) by interrupting Windows boot three times, as described in Method 1.

Step 2: In WinRE, navigate to Troubleshoot > Advanced options > Startup Repair.

Step 3: Follow the on-screen instructions to allow Windows to automatically detect and repair startup issues. Once the process completes, restart your computer and check if the issue is resolved.

Method 3: Repair Corrupted System Files (SFC and DISM)

Step 1: Boot into Safe Mode with Command Prompt by following the steps in Method 1, but select Command Prompt from the Advanced options menu.

Step 2: In the Command Prompt window, type the following command and press Enter to run the System File Checker (SFC):

sfc /scannow

Step 3: After SFC completes, run the DISM tool to repair the Windows image:

DISM /Online /Cleanup-Image /RestoreHealth

Once both scans finish, restart your computer and check if the issue is resolved.

Method 4: Disable Driver Signature Enforcement

Step 1: Boot to Windows Recovery Environment (WinRE) as described earlier.

Step 2: Navigate to Troubleshoot > Advanced options > Startup Settings. Click Restart.

Step 3: After the restart, press F7 to disable Driver Signature Enforcement. This setting allows Windows to boot even if a problematic unsigned driver is causing the issue.

If this resolves the issue, uninstall or update the problematic driver through Device Manager.

Method 5: Rebuild Boot Configuration Data (BCD)

Step 1: Boot into WinRE and select Troubleshoot > Advanced options > Command Prompt.

Step 2: In Command Prompt, execute the following commands one by one, pressing Enter after each:

bootrec /fixmbr
bootrec /fixboot
bootrec /scanos
bootrec /rebuildbcd

After completion, restart your computer to verify if the issue is resolved.

Method 6: Perform System Restore

Step 1: Boot into WinRE and select Troubleshoot > Advanced options > System Restore.

Step 2: Choose a restore point from before the error started occurring, and follow the on-screen instructions to restore your system.

System Restore will revert your system to a previous working state without affecting personal files.

Method 7: Uninstall Recent Windows Updates

Step 1: Boot into WinRE and select Troubleshoot > Advanced options > Uninstall Updates.

Step 2: Choose to uninstall the latest feature update or quality update.

After uninstalling the update, restart your system to see if the error is resolved.

Method 8: Reset Windows

If none of the above methods work, resetting Windows can resolve persistent system issues.

Step 1: Boot into WinRE and select Troubleshoot > Reset this PC.

Step 2: Choose either Keep my files or Remove everything. Follow the on-screen instructions to reset your Windows installation.

After the reset, your system should boot normally without the 0xC000021A error.

Resolving the 0xC000021A error may require multiple troubleshooting steps. Always ensure you have recent backups of your important data before performing major repairs or resets. If the issue persists despite all efforts, consider consulting a professional technician for further assistance.