How To Fix Error 0xc000021a For Windows 8 & 10

During the release of Windows 8 and 10, many consumers were facing multiple technical problems. These problems were either related to the drivers or the operating system itself. Updates were released, and with updates, many new features were introduced that solidified Windows’ foothold in the computer operating system market.

We’ve come a long way from the early Windows days, but even though Microsoft has done its best to make sure all errors and bugs were resolved over time, many of them persist today due to either negligence or lack of viable solutions.

One such error that has tormented and frustrated many Windows users is the dreaded 0xc000021 error. Have you encountered this error yourself? Are you close to tearing your hair out, trying to figure out how to solve the problem? Well don’t worry, there’s no need to save up for a wig, because I’ve got your answers! Read on to fix your problem.

Are you experiencing another Windows error code and don’t know how you got here? No worries, Error Codes Pro has the ultimate windows error list that can surely help you find the answers you need to diagnose that pesky problem! More specifically, if Error Code 0xc000007b is what you’re up against, we’ve got a detailed guide to get you out of the darkness (my old friend).

What Does 0xc000021 even mean in human terms, anyway?

The 0xc000021 error states that the computer’s operating system cannot be initialized because a crucial file that assists in booting the OS is either missing or damaged.

So great. There’s something wrong with the very foundation of your computer. When this error pops up on your screen and you’re left feeling helpless, don’t panic! Ask yourself, what could have damaged these files? Here are some suggestions:

  • A forced shutdown of the system.
  • A damaged hard disk.
  • Corruption caused by virus.
  • A glitch when updating Windows.

What crucial files, if damaged, can cause the 0xc000021 error?

Winlogon.exe and csrss.exe are the files that, if damaged, can represent this error. Winlogon.exe, as the name would suggest, is a file that shows the login and logout window on your computer screen when Windows is initialized. This file can also be corrupted when files of the previous update and the new update are not the same. It can also be altered by third party software (AKA…a virus) if they are granted the modification and can be corrupted by the virus itself.

Csrss.exe is a file that is responsible for making a connection with the Microsoft server or the client. If this file is corrupted or damaged, then this error may also occur during the booting of the Windows.

So I Know What I’m Up Against Now…Let’s Fix It!

You’ve got a few options when it comes to fixing Error 0xc000021a. Read through each, pick the one you’re most comfortable with, and let’s begin.

Booting Windows Manually by Force Drivers

Booting into safe mode may not work in most cases, and when you’re computer’s on the fritz so much that you have to be able to get into the back end of things, that’s not a good sign. So in this situation, to launch Windows manually, you will be required to use force drivers to get the signature disabled so that Windows does not automatically boot to the bootloader sequence. For this, you will need the Windows installation disc or a Windows bootable USB. Don’t know what a bootable USB is or how to acquire one? Check out Bootable USB’s site to learn how.

Got your bootable USB or Windows installation disc? Great! Let’s do this.

First, restart your PC with the disc already inserted or USB attached to the USB port. This will take you to the Automatic Repair screen when booting, where you will have multiple options.

From there, choose the Troubleshoot option. This will get you to the next phase, where you will select Advanced Options.

Now you will be given five options on the next screen. Select Startup Settings option. This board controls the booting sequence and other startup checks. Select Disable driver signature enforcement.

Your computer should now restart with whatever options you have selected for booting.

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Reset The Computer’s BIOS

This method is more physical than the software interaction. Many users have suggested this approach since resetting the BIOS of the system appears to be a good way for the error to be fixed. For this, you will be required to open your computer’s side panel, which would give you a direct view of the motherboard.

NOTE: This method may not work on laptops since the motherboards of laptops and notebooks are not accessible for configuration changes. If you are facing such problems with your notebook and wish to use this method, it is recommended that you either take your laptop to a technician or contact your laptop provider.

First of all, turn off your PC. After that, remove the power cables that are supplying electricity to the CPU. Remove the CMOS battery on the motherboard as well. The CMOS battery is located in a different location and section of the motherboard. Read your computer’s manual to get a more detailed description of where everything is located. The CMOS battery is round, shiny and flat in nature like a tablet. Pull it out carefully.

Leave the computer at rest for at least 3 to 5 minutes. This will drain all the power out that is still circulating in the PC. Afterward, it will refresh the BIOS to its default, meaning all your manual modifications in the BIOS will reset as well. Any password protection will also be nullified.

Reattach all the cables and the CMOS battery back in its place. Start your PC. When you’re asked whether you want to restore the BIOS to default, click “Yes.”

“The PC has improved the world in just about every area you can think of. Amazing developments in communications, collaboration and efficiencies. New kinds of entertainment and social media”. – Bill Gates

Registry Hive Files and Windows Built-in Backup Replacement

Many viruses are designed to attack the registry hive files of Windows. They mostly attach themselves with the crucial keys of registry hive, and when you try to run any antivirus application, they will destroy the crucial keys either along with themselves or to protect themselves from being removed. Corrupted registry keys could be keeping your computer from working properly itself; read this article to learn more about Runtime Error 203.

Windows registry hive gives applications a hierarchy. Windows requires these keys to run themselves, and since your PC cannot boot Windows, you cannot use “Registry Editor” to fix this- but don’t panic! To work around this error using this method, you will be required to use Command Prompt, which will be possible after booting through the Windows Recovery Environment.

If you are going to use this method, you will be required to install the Windows Recovery Environment first. To install the Windows Recovery Environment, you will need the Windows Installation disc or the USB. Note that the Windows version in the Windows Installation PC should be the same version that is currently present on your computer.

Plug in the Windows installation USB or insert the Windows installation disc in your PC and restart the computer. As soon as the computer starts booting up, click the default button for the BIOS and change your boot sequence. This might be tricky because every motherboard brand has its BIOS interface. You can search for your BIOS utility interface boot sequence on the internet and change the boot sequence from HDD/SDD to whatever Windows installation media you are using.

Press “Esc” on the keyboard until you receive notification that you are about to leave the BIOS utility panel. You will receive options regarding the changes that you have made. Select “Save Changes and Exit.”

Your PC will reboot, and you will be prompted to press any key to boot the media drive that you selected in the boot sequence.

  • Press any key.
  • Select whatever language you prefer for the setup, the timezone you prefer and your key out input layout and proceed by clicking “Next.”
  • You will be prompted to a window where you will receive the button saying, “Install now.”
  • You will also receive a hyperlink text saying, “Repair your computer.” It will be present on the bottom left corner of the screen.
  • This next section will be where you will find the Startup Options. Once you are on this panel:
  • Click on Troubleshoot – Advanced Options, then click on Command Prompt.

Type “C:” (without quotations) or whatever directory label in which you have installed your windows, and then press Enter key. This will take you to the directory in which Windows is installed.

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Type cd windows\system32\config into the Command Prompt and press the Enter key. This will direct you to the main core directory of the Windows. Next, type “dir” (without quotations again!), which will display all the available folders and files in the existing directory.

This process will be tiresome and lengthy, as you will rename all the files (not folders) in the folder. Type “ren (file’s name) (file’s name).old” (you guessed it…without quotations) command and press Enter key.

Once you rename all the files in the directory, you have created a backup of all your data. Now type in cd RegBack into the command Prompt and Enter.

Type “dir” into the Command Prompt Windows and press Enter to display all the files in the directory again.

Now type the following commands one by one into the command prompt.

Copy/Y software

Copy/Y sam

Copy/Y system

Once this is done, close the Command Prompt, and exit the Window Recovery Environment by simply typing Exit and pressing the Enter key. Remove the Windows Installation device and read the boot sequence to boot the drive in which the Windows is installed. The 0xc000021 error should not be displayed now.


If you successfully solved your error 0xc000021a problem, congratulations! You put in some major work today and deserve a pat on the back- or maybe some extra screen time. Be sure to do a thorough antivirus scan and root out the cause!

Don’t forget to visit us again if you have any questions about other errors, or if you just want to know what all those HTTP error codes mean. Be sure to check out my other articles on Error Codes Pro- who knows, you might see something you could use!

If you’re still stuck with a bum computer that won’t boot up, don’t give up just yet. I’ve got some pro tips that might help point you in the right direction.

Pro Tips Galore:

  1. If you’ve decided to go with option one and are using a bootable USB, be sure you installed the correct information for your operating system and version of Windows. It sounds silly, but double checking every step you take could save you time in the long-run.
  2. If you’re having trouble where you think you shouldn’t, contact Windows’ customer service and let them know what’s happening. They might be able to point you in the right direction, or at least take down your information so they can work on fixing this error.
  3. If you truly feel like you’ve done all you can, or if you don’t think you can tackle this error yourself without becoming the equivalent of a bull in a china shop, I encourage you to take your computer to a repair shop and let the pros do the work for you. Sure, it’ll cost you, but you’ll walk out with a computer you can actually use- that’s a win if you ask me!

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