The blog of Windows Wally, a Windows Support Technician helping common people solve frustrating computer problems.



How To Fix STOP Error 0xc000021A In Windows 8.1

Reader Question:
“Hi Wally, My laptop is acting up. Its Windows 8.1 and when it starts, it says Error 0xc000021A !” – Brenda G., USA

Before addressing any computer issue, I always recommend scanning and repairing any underlying problems affecting your PC health and performance:

  • Step 1 : Download PC Repair & Optimizer Tool (WinThruster for Win 10, 8, 7, Vista, XP and 2000 – Microsoft Gold Certified).
  • Step 2 : Click “Start Scan” to find Windows registry issues that could be causing PC problems.
  • Step 3 : Click “Repair All” to fix all issues.

Setting up weekly (or daily) automatic scans will help prevent system problems and keep your PC running fast and trouble-free.

Wally’s Answer: Lets face it, getting a Blue Screen of Death error when you start the computer is the worst. You decided to do something on the computer and it fails on you, what a drag :(

IRQL_NOT_LESS_OR_EQUAL - Cover -- Windows Wally

Problem

When the computer starts it shows a blue screen with the error 0xc000021A.

Cause

Error 0xc000021A usually occurs when the files Winlogon.exe or Csrss.exe are damaged.

Winlogon.exe is responsible for handling the login and logout processes.
Csrss.exe belongs to Microsoft Client or Server ‘Runtime Server Subsystem’.

The aforementioned files may be damaged because:

  • System files have been mismatched
  • Incorrect device drivers have been installed
  • Third-part software is missing some files

Solution

Here are some ways to fix the Error 0xc000021A problem:

Clean Boot In Safe Mode

When the computer does not boot properly, it will eventually start showing the Automatic Repair screen when you start the computer.

  1. In the Automatic Repair screen, click Advanced options
  2. Click Startup Settings
    Error 0xc000021A - Safe Mode - Startup Settings - 1 -- Windows Wally
  3. On the Startup Settings screen, click the Restart button
  4. Enable Safe Mode with Networking

If the Automatic Repair screen does not appear for you then use the following instructions:

  1. Use a Windows 8 or 8.1 CD/DVD/USB to boot your computer.
  2. On the screen that appears click the button labeled Next
  3. Click the link labeled Repair your computer
  4. Click Troubleshoot > Advanced options > Command Prompt
  5. In the Command Prompt window, type:
    bcdedit /set {default} bootmenupolicy legacy
    and press Enter
  6. Now, take the CD/DVD/USB out and restart the computer.
  7. When the computer restarts, keep pressing the F8 key repeatedly and you should see the Advanced Boot Options screen
    Error 0xc000021A -- Advanced Boot Options - Windows 8 -- Windows Wally
  8. Select Safe Mode from the list

If the computer starts in Safe Mode successfully, then move forward with the following procedure to fix the boot process:

Disabling Windows Services

  1. Press Windows Key + R > type msconfig > press Enter (or click OK)
    IRQL_NOT_LESS_OR_EQUAL - msconfig -- Windows Wally
  2. Click the Services tab
  3. Make sure that Hide all Microsoft services is checked.
  4. Click Disable All and click Apply
    Explorer Crashes - msconfig - Services tab - Disable All -- Windows Wally
  5. Click the Startup tab
  6. Click Open Task Manager
    Explorer Crashes -- msconfig - Startup tab - Open Task Manager - Windows Wally
  7. Disable all items one by one and close the Task Manager
    Explorer Crashes -- Task Manager - Startup tab - Disable - Windows Wally
  8. Click OK to close the System Configuration window.

Now restart your computer. If Windows 8.1 tarts normally then it means that one of the startup programs or services was at fault. Start enabling the ones that you think are okay and restart the computer again. Eventually you should be able to find the culprit and either keep it disabled or uninstall the program.

Fixing Windows 8.1 System Files

If you still can’t get into Windows 8.1, you should use this method to check Windows 8.1 system files.

  1. Insert the Windows 8/8.1 installation DVD/USB or Recovery Disk
  2. Restart your computer
  3. Click the Next button
  4. Click the Repair your computer link
  5. Click Troubleshoot > Advanced Options > Command Prompt
  6. In Command Prompt type sfc /scannow > and press Enter

Using System Restore

System restore is used to recover system files and settings from the past. It can be used to replace damaged and corrupt files in the computer. Click here you learn how to make a system restore point.

Reverting Windows Updates To Fix Error 0xc000021A

Probably the most common way that a blue screen error occurs is when a user turns off a computer while its applying updates. The user may forcibly turn off the computer when it won’t shut down because its waiting for updates to be applied. Here’s how to revert the failed Windows update:

  1. Insert the Windows 8/8.1 installation DVD/USB or Recovery Disk
  2. Restart your computer
  3. Click the Next button
  4. Click the Repair your computer link
  5. Click Troubleshoot > Advanced Options > Command Prompt
  6. In Command Prompt type dism.exe /image:C:\ /cleanup-image /revertpendingactions (here C is your computer’s system drive)
    Error 0xc000021A -- Boot - Command Prompt - Revert Windows update - Windows Wally
  7. Press Enter to run the command and revert the update.

How To Refresh Windows 8.1

This feature will refresh Windows 8 but it will not delete your personal files or installed programs.

  1. Insert the Windows 8/8.1 installation DVD/USB or Recovery Disk
  2. When you get to the setup screen, click Next
  3. Click Repair your computer
  4. In Advanced Startup options, click Troubleshoot
  5. Click Refresh your PC

How To Reset Windows 8.1

If nothing else works then you can reset Windows 8/8.1. This should most certainly solve the Error 0xc000021A problem if it is Windows or software related.

  1. Insert the Windows 8/8.1 installation DVD/USB or Recovery Disk
  2. When you get to the setup screen, click Next
  3. Click Repair your computer
  4. In Advanced Startup options, click Troubleshoot
  5. Click Reset your PC

Is Your PC Healthy?

I always recommend to my readers to regularly use a trusted registry cleaner and optimizer such as WinThruster or CCleaner. Many problems that you encounter can be attributed to a corrupt and bloated registry.

Happy Computing! :)

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About the Author

Windows Wally is a helpful guy. It’s just in his nature. It’s why he started a blog in the first place. He heard over and over how hard it was to find simple, plain-English solutions to Windows troubleshooting problems on the Internet. Enter: Windows Wally. Ask away, and he will answer.