The 0xC000021A error can occur if Winlogon.exe or Csrss.exe stops working. This happens if:

There were corrupt system files in the computer.

There was a failed upgrade.

Incomplete installation of a software program.

Unplug all external devices like flash drive, printer and scanner etc., (except mouse and keyboard) connected to the computer and restart the system to check if the computer boots to the desktop screen.



If you are still not able to boot, the usual fix for this is to repair your BCD in Command Prompt by Booting from your Installer and choosing Repair My Computer.



Let us try to repair the Windows using the ISO file.

Refer to the following link to download Windows 10 ISO file and create installation media.

https://www.microsoft.com/enus/softw...



Once your media is ready follow the steps.



1. Insert the Windows 10 DVD and restart your computer
2. Boot from the DVD.
3. Choose your language and click next.
4. Click Repair Your Computer and then select Command Prompt and try the following commands:
bootrec /fixMBR
bootrec /fixBoot
bootrec /rebuildBCD



Restart the computer.



Disclaimer: Modifying BIOS/ complementary metal oxide semiconductor (CMOS) settings incorrectly can cause serious problems that may prevent your computer from booting properly. Microsoft cannot guarantee that any problems resulting from the configuring of BIOS/CMOS settings can be solved. Modifications of the settings are at your own risk.

Fixes in user mode device driver user, system service, or third party: Due to the 0xc000021a process verification error in user mode, the most common cause is a thirdparty app. If an error occurs after installing a new or updated device driver, system service, or thirdparty applications, the new software must be removed or disabled to isolate the cause. Contact the software manufacturer regarding a possible upgrade.

The solution to the problem does not match the file system: If you just restore from a hard drive backup, check for an updated software backup/restore available from the manufacturer.

These steps can help gather additional information about error code 0xc000021a.

Look at the last installed app. To access "Uninstall or change a program" in the applications and administration control panel installed on the date of installation.

Check the System log in Event Viewer for additional error messages that might help identify the device or driver that caused the error. For more information, see Open Event Viewer. Look for a fatal error in the system registry, which occurred in the same time window with a blue screen.

These steps can help resolve this issue.

Use the System File Checker tool to fix missing or corrupt system files. System File Checker is a Windows utility that allows users to check for corruption in Windows system files and recover corrupted files. Use the following command to run the System File Checker Tool (SFC.exe).

to entertain

copy
sfc /scannow
For more information, see Use the File Checker tool to fix missing or corrupt system files.

Run a virus detection program. The virus can infect all types of hard drives formatted for Windows, and disk corruption can create a system for checking code errors. Be sure to start the main virusdetector in the program registry to check for infection.

Make sure that the latest service pack is installed on the system. To detect the service pack, if any, installed on your system, click Start, then Run, type winver, and press ENTER. The About Windows dialog box displays the Windows version number and the service pack version number, if installed.

Use safe mode to fix 0xc000021a

Remember to use Safe Mode to isolate items to solve problems and if using Windows is required. The insurance fee uses only the minimum services and drivers necessary to start Windows Mode. To enter safe mode, update the security settings. Select Recovery Advanced startup to boot into maintenance mode. In the menu that appears, select Debugging Advanced Startup Settings Restart. When the screen restarts to configure Windows startup, select an option, 4, 5, or 6 to start in safe mode.

Safe mode may be available by pressing the start function such as F8. Refer to manufacturer information for specific startup options.



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