You know there are different kinds of Windows errors that can appear while you’re using a computer. Some errors are followed by an error number and a short error message to describe the problem you're your system runs into. Well, a fatal system error means that the error shows up on your system is serious and it may cause system crash & BSOD.

What Is Fatal System Error

Literally, fatal system error refers to a serious and terrible system error that will damage your system and may lead to data loss. A fatal system error is also known as a stop error, system crash, kernel error, or bug check. The fatal system error will show up whenever your operating system stops working (can’t operate safely).

There are many people discussing Windows 10 fatal system error. Before talking about it, I’d like to introduce system error briefly in advance.

fatal system error

If you need to back up system, recover files, or troubleshoot disk problems, MiniTool Solution can be a good assistant.

What Is System Error Code

The system error code is also called error code or an operating system error code; it actually refers to the error number which is followed by a short error message in some cases. The error code appears in Windows to inform users, especially the developers that there’s a particular problem showing up. System error code contains many predefined error codes and error messages that are created by software programmers to tell other people when they are experiencing a problem.

What Is System Error And How Do You Fix It?

In other words, the system describes the issue it has currently by giving an error code in order to let people, especially the software developers, know what’s happening. In this way, they may figure out a way to fix it ASAP!

Note: The system error code in Windows is not the same as a Windows STOP code, a POST code, an HTTP status code, or a Device Manager error code. The system error codes are generic so they can be applied to different circumstances. What’s more, the same Windows 10 system error may be used in a lot of different cases to show you what problem you have.

Just as its name implies, the fatal system error refers to the one which is terrible and may lead to serious problems like the blue screen of death (BSOD). A fatal system error may occur suddenly due to a kernel-mode driver with either the KeBugCheck or KeBugCheckEx function.

Related reading:

Many people reported they run into a fatal device hardware error: the request failed due to a fatal device hardware error, you should read the following link carefully to know how to deal with it.

Easy Fix: The Request Failed Due To A Fatal Device Hardware Error
Easy Fix: The Request Failed Due To A Fatal Device Hardware Error

I find the request failed due to a fatal device hardware error is not a rare problem, so I decided to dedicate the best solution for you.

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Fatal System Error c000021a

Let’s take a look at the fatal system error blue screen c000021a, which is one of the most popular fatal system errors you may encounter.

STOP: c000021a {Fatal System Error}

The Windows Logon Process system process terminated unexpectedly with a status of 0x00000403 (0×00000000 0×00000000).

The system has been shut down.

Restart and set the recovery options in the system control panel or the /CRASHDEBUG system start option. If this message reappears, contact your system administrator or technical support group.


The exact error message of Windows STOP c000021a Fatal System Error may be slightly different. But you need to realize what happened when this blue screen fatal error shows up on your PC: the Windows kernel has detected that either Winlogon.exe or Csrss.exe service processes went wrong (have stopped responding or have failed to load). The system will be stopped immediately and the corresponding fatal system error message will be shown on the PC screen.

Main reasons for causing fatal error c000021a:

  • A hardware failure occurs (for instance, the RAM is faulty).
  • Hardware drivers are corrupted or missing.
  • The Windows service pack is not installed properly.
  • Too many invalid and bad registry keys are found.
  • There’s trouble with the Power Supply Unit (PSU).
  • Windows System Restore is not working while rolling back.
  • Kernel level conflicts are caused by third-party programs or applications.
  • The system files are corrupted or missing because of virus/malware or improper shutdown.

Main solutions to fixing Windows fatal error c000021a:

  • Take out the battery and put it back again.
  • Update the computer device drivers to the latest versions.
  • Execute CHKDSK command in Command Prompt window.
  • Arrange a test on your computer RAM or swap it out.
  • Run a full scan of the systems registry.
  • Boot Windows into Last Known Good Configuration.
  • Boot PC to some external Media.
  • Restore the system to a previous state by making use of System Restore.
  • Uninstall the programs and applications that you have installed on PC recently.
  • Use Windows Startup Repair to scan, detect, and repair problems.
  • Replace the Power Supply Unit (PSU).
  • Repair from the Windows disk (for Windows XP users).
  • Backup files and reinstall the Windows system. This is the trump card, but also the last resort.


The CHKDSK command may delete your files sometimes according to users’ feedback. If you want to get them back, you should read this page carefully since it tells you how to recover data after CHKDSK in two useful ways.

Files Get Lost After CHKDSK? Now Recover Them in Three Ways
Files Get Lost After CHKDSK? Now Recover Them in Three Ways

Does your files get lost after CHKDSK? Here are ways to help your recover CHKDSK deleted files in few steps.

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How to Fix Windows 10 Fatal Error

In this part, I will introduce 8 ways to help fix the fatal error on a Windows 10 PC. The steps to fix Windows fatal error in other systems are basically the same.

#1. Replace Corrupted System Files

As mentioned earlier, having corrupted system files is a general cause of fatal system error. If you can find a way to replace the corrupted files, you can solve the problem easily. Some people said they had fixed the issue successfully by replacing files including winlogon, msgina.dll, and Userinit.exe.

What you should do:

  1. Find another computer that runs the same version of Windows 10.
  2. Open File Explorer and go to this path – C:\Windows\System32.
  3. Look for the winlogon, dll, and Userinit.exe files.
  4. Press Ctrl + C to copy certain files.
  5. Open the same directory on your computer.
  6. Press Ctrl + V to paste these files and let them replace the corrupted ones.


How to recover files you’ve deleted mistakenly or lost suddenly?

Step 1: get and install MiniTool Power Data Recovery (don’t save it to the drive that includes the deleted/lost data).

MiniTool Power Data Recovery TrialClick to Download100%Clean & Safe

Step 2: run the recovery software and choose an option from the left sidebar. Choose This PC to recover data from existing local drives or choose Hard Disk Drive to recover files from a lost partition.

Step 3: double click on the target disk/partition to start a full scan on it.

Choose an option from the left sidebar

Step 4: wait for the scan. Then, browse the found files one by one to pick out what you need.

Step 5: click on the Save button. Then, choose a safe storage path and click OK.

Step 6: wait until all the files have been recovered to the appointed place.

Please get a license to register MiniTool Power Data Recovery; otherwise, you won’t be allowed to recover the deleted/lost files.  As for how to recover data from PC won’t boot, I’ll talk later.

If you also have lost files waiting to be recovered, you should follow the steps mentioned here to get them back as soon as possible. If you find this is useful, please share it out to help more people get rid of the data loss dilemma.Click to Tweet

#2. Disable Driver Signature Enforcement

  1. Press the power button on your PC.
  2. Press it again right after the Power-On Self-Test (POST) to shut down the computer.
  3. Repeat step 1 and step 2 twice to enter the Windows Recovery Environment (Windows RE).
  4. You’ll see the Preparing Automatic Repair window.
  5. Select an account and enter the corresponding password if required. Then, click Continue.
  6. Click on the Advanced options button to continue with the Advanced startup environment.
  7. Select Troubleshoot > Advanced options > Startup Settings one by one.
  8. Press F7 on your keyboard to choose Disable driver signature enforcement.

Preparing Automatic Repair

#3. Turn to SFC Scan

You may as well try the SFC scan which is designed to repair corrupted files. (How to recover corrupted files efficiently to minimize losses?)

  1. Click on the Start button in the lower left corner.
  2. Navigate to the Windows System folder and expand it.
  3. Right click on Command Prompt and choose More -> Run as administrator.
  5. Press Enter on your keyboard.
  6. Wait until the scan is finished. It will repair the errors for you automatically.

SFC scan

#4. Run CHKDSK Command

  1. Also, you need to run the Command Prompt tool as an administrator.
  2. Type chkdsk /r C: into the window and hit Enter.
  3. Wait for the command to finish.


How to recover files with Command Prompt utility?

#5. Use DISM Command

  1. Insert your Windows 10 installation media to the computer.
  2. Boot from this installation media properly.
  3. Press Shift + F10 at the same time to open Command Prompt window.
  4. Type or copy & paste this command into it: dism /image:c: /cleanup-image /revertpendingactions.
  5. Press Enter on the keyboard and wait for the command to finish.
  6. It will help you solve the problem if any errors are found.

DISM command

You can also repeat step 1 to step 3 mentioned in the previous method to run Command Prompt as an administrator and run the DISM command.

How to fix when the DISM failed on Windows 10/8/7 computer?

#6. Copy & Paste the Moved Files

Warning: This process is a little bit dangerous since you need to copy files and paste them to the Windows 10 installation directory. However, if you really need to fix the fatal error on Windows 10, it worth a try. I strongly recommend that you backup your drive/files before copying any files by using MiniTool ShadowMaker, in case of any unexpected error.
  1. Boot your Windows 10 computer from Linux media.
  2. Locate the hard drive accurately. Then, access it.
  3. Look for the folder named 000 or several found folders.
  4. Copy all the files inside the folder (press Ctrl + A to select all items and press Ctrl + C to copy them).
  5. Go to open C:\Windows\System32 and press Ctrl + V to paste the files here.

Copy and paste moved files

How To Recover Data From Windows.old Folder Quickly & Safely?

#7. Repair the Registry by Using Backup

  1. Open File Explorer and go to C:\Windows\System32\config.
  2. Select Default, Sam, Security, Software, and System files by holding Ctrl.
  3. Press Ctrl + C to copy them. Then, go to another location to paste them by pressing Ctrl + V. (These steps are not necessary, but they are important for backup.)
  4. Go to C:\Windows\System32\config\RegBack this time.
  5. Press Ctrl + A to select all the items and press Ctrl + C to copy.
  6. Go back to C:\Windows\System32\config and press Ctrl + V to paste.

How to fix when you can’t copy or move files?

What if you can’t access your system at all? Of course, you should boot into Safe Mode and finish these steps.

How to recover data when PC can’t boot?

  1. Find another computer. Buy a license for MiniTool Power Data Recovery (make sure it includes Snap-in WinPE Bootable Builder by looking at the comparison).
  2. Get the setup program, install it, and then launch.
  3. Copy & paste your license to register for a full edition.
  4. Click on the Bootable Media button in the lower left corner.
  5. Follow the on-screen instructions to create a bootable USB drive or CD/DVD by using MiniTool Media Builder.
  6. Remove the bootable disk from the current computer and connect it to the PC that won’t boot.
  7. Enter BIOS and change the boot order to boot from this disk.
  8. Select the first option in MiniTool PE Loader window.
  9. Choose the target drive to scan -> browse scan result -> save needed data to an external storage device.

Bootable Media

Launch software

Please don’t worry when you come across a fatal system error on Windows 10 (or other systems). This post tells you how to fix the error step by step in different ways. Besides, it teaches you how to recover data from a PC that refuses to boot.Click to Tweet

#8. Reset Windows 10

  1. Restart your PC for a few times during startup in order to enter Automatic Repair.
  2. Choose Troubleshoot, Reset this PC, and Remove everything one by one.
  3. Please insert your installation media if required.
  4. Choose Only the drive where Windows is installed and then Just remove my files.
  5. Finally, click on the Reset button.
  6. Follow the instructions and wait for the reset process to accomplish.

Remove everything

People also said they have fixed the fatal error by the following methods:

  • Rollback drivers to the previous version in Device Manager.
  • Uninstall all the applications, programs, or drivers installed recently.
  • Update the system, programs, and drivers to the latest versions.
  • Check the hardware for errors, including motherboard, CPU, RAM, and so on.

Final Thoughts

Though fatal system error sounds serious and may cause your system to fail to boot, you still don’t need to worry too much. It doesn’t matter you are encountering c000021a or other codes indicating the fatal error; there are always useful methods to help you solve the problem.

In the previous content, I mainly introduce 8 ways to fix Windows fatal error. In addition, 4 other solutions are given as a bonus. What’s more exciting is that it demonstrates the steps to recover data from a Windows 10 PC and from a PC that won’t boot successfully.

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