FIX: Windows Defender Error 0x800b0100

Teodor Nechita
by Teodor Nechita
Software Managing Editor
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Windows 10 is an extremely versatile and self-sufficient OS. One of the biggest testimonies to that fact is that it comes with a very efficient built-in protection system called Windows Defender.

However, things don’t always go smoothly for Windows Defender. For example, some users have reported receiving an error code 0x800b0100when trying to launch it.0x800b0100

This error will prevent you from turning on Windows Defender, rendering you defenseless.

Since this is a very problematic issue that completely blocks the functionality of a vital Windows component. That is why we’ve created this step-by-step guide that will show you exactly what you need to do.

How do I fix Windows Defender Error 0x800b0100?

1. Perform a Clean Boot

  1. Press Windows + R
  2. Type in msconfig
  3. Go to the Services tab
  4. Check the option that says Hide All Microsoft Serviceshide all windows services
  5. Click Disable All
  6. Go to the Startup tab
  7. Select the Task Manager
  8. Right-click and select Disable for all processes found in the Startup tab
  9. Press OK to confirm the changes
  10. Reboot your PC for the changes to take effect

By following these steps, you should be able to see whether a third-party application was blocking Windows Defender. If this is indeed the cause, reverse the changes you’ve made for each program.

It is best if you reverse the process one at a time to determine which program exactly is causing the issue.

2. Check your Windows Defender Service

  1. Press Windows + R
  2. Type in msconfig
  3. Locate Windows Defender
  4. Double-click the following items:
    • Windows Defender Service
    • Windows Defender Advanced Threat Protection Service
    • Windows Defender Network Inspection Service
  5. Make sure the Startup Type is set to Automatic and that the service is Started

4. Check your PC for Malware

Quite ironically, this Windows Defender can be caused by an already-present infection of your Windows 10 PC. As such, simply install a very good third-party antivirus tool to perform a complete scan and cleanup of your Windows system.

Looking for a good antivirus tool? Check out this article for our top picks

5. Perform an SFC

Deployment Image Servicing and Management

  • Press Windows key + X, then select Command Prompt (Admin)
  • Enter the following command in cmd: DISM.exe /Online /Cleanup-Image /RestoreHealth
  • Hit Enter
  • After the procedure is completed, type the following in the cmd: 
    • sfc /scannow
  • Let System File Checker run
  • Restart your PC

6. Perform a DISM

  1. Press Start
  2. Type in cmd.exe
  3. Right-click the Command Prompt and choose Run as administrator
  4. Type in the following line:
    • DISM /Online /Cleanup-Image /RestoreHealthdism
  5. Press Enter to run the command
  6. Wait for it to perform the scan, it can take about five to ten minutes, sometimes more.
    • If the progress bar gets stuck on 20 percent, don’t worry, that’s perfectly normal, you just need to be patient.
  7. After DISM has finished its scan, restart your computer

By following these steps, you should be able to have Windows Defender up and running again and enjoy a malware-free PC experience.

Which of the methods listed above worked for you? Let us know in the comments section below.


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