0x00000021 BSoD: What is it & How to Fix it

Our readers have reported coming across 0x00000021 – QUOTA_UNDERFLOW Blue Screen of Death error. This basically puts their PCs in a restart loop. Windows 10 users are the ones that are affected because of this 0x00000021 BSoD error among other BSoD problems.

Why am I getting the 0x00000021 – QUOTA_UNDERFLOW error?

After going through various user reports and forum posts, we have listed down some of the most common reasons that could trigger the 0x00000021 QUOTA_UNDERFLOW BSoD error on your PC:

• Outdated drivers – If your PC has outdated drivers then not only the performance won’t be optimal but you will face multiple issues.
• Malware infections – Virus or malware can cause great damage to the system files thereby causing issues such as the 0x00000021 QUOTA_UNDERFLOW BSoD error.
• Corrupt system files – Chances are some important system files are corrupt or are missing from your PC, which is causing the problem.
• Hard disk errors – Hard disk malfunction or bad sectors can also give rise to multiple Blue Screen of Death errors.

Let us check out the solutions to resolve the 0x00000021 – QUOTA_UNDERFLOW error.

How can I fix the 0x00000021 – QUOTA_UNDERFLOW BSoD error?

1. Perform a Startup Repair

1. Turn off and on your PC three times using the Power button to boot into the Advanced Startup environment.
2. Click on Next, then select the Repair your computer option.
3. Hit the Troubleshoot option.
4. Click on Advanced options.
5. Hit the Startup Repair option.
6. Select your account, enter your password, and click Continue.

You may also use a dedicated tool and fix the BSoD or startup problem pretty easily. For that, we have listed the best boot repair tools that you can use on your Windows 10 PC.

2. Fix corrupt system files

1. Enter the Advanced Startup environment as instructed in Solution 1.
2. Click on Next and choose the Repair your computer option.
3. Hit the Troubleshoot option.
4. Click on Advanced options.
5. Select Command Prompt.
6. Type the below command and press Enter. sfc /scannow
7. Wait for the process to complete.
8. Type the below commands and press Enter after each one. DISM.exe /Online /Cleanup-image /Scanhealth DISM.exe /Online /Cleanup-image /Restorehealth DISM.exe /online /cleanup-image /startcomponentcleanup
9. Restart your PC.

You can easily resolve the system file corruption by using the above two commands and hopefully fix the 0x00000021 – QUOTA_UNDERFLOW error.

Besides this, you can try a specialized repair tool that can fix broken system files automatically in less than 5 minutes.

3. Update the drivers

1. Press the Win key to open the Start menu.
2. Open Device Manager.
3. Expand each section.
4. Double-click on your driver.
5. Click on the Driver tab.
6. Select the Update driver option.
7. Choose Search automatically for drivers option.
8. Restart your PC.
9. Follow the same process for every driver.

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4. Scan your PC for viruses

1. To open the Start menu, press the Win key.
2. Open Windows Security.
3. Select Virus & threat protection.
4. Click Quick Scan.
5. You can also click on Scan options and select Full scan for a deep scan.
6. Restart your PC after the process is finished.

Using the Windows Security tool, you can remove the virus or malware from your PC. However, it isn’t proven to be that effective as compared to dedicated antivirus tools.

We have compiled a list of some of the best antivirus software to protect your PC from various malware and also resolve issues such as 0x00000021 – QUOTA_UNDERFLOW error.

5. Perform a System Restore

1. Enter the Advanced Startup environment as instructed in Solution 1.
2. Click on Next.
3. Choose the Repair your computer option.
4. Select the Troubleshoot option.
5. Choose Advanced options.
6. Choose the System Restore option.
7. Click Next.
8. Choose the restore point and hit the Next button.
9. Hit the Finish button.

You can perform the system restore in order to take your PC back to a state where everything was working without any issues.

That is it from us in this guide. Windows 11 users are reportedly coming across the Black Screen error, which you can easily fix by following the solutions mentioned in our guide.

Let us know in the comments, which solution fixed the problem for you.