unable to turn on Microsoft defender Antivirus

If you are unable to turn on Microsoft Defender Antivirus and selecting quick scan results in no response, it may be due to several reasons. Here are some steps you can take to troubleshoot the issue:

1. Check for Non-Microsoft Antivirus: If you have a non-Microsoft antivirus installed, Microsoft Defender Antivirus may be automatically turned off. You can check this by going to the Services app and looking for the status of the Microsoft Defender Antivirus Service. If it is set to manual and cannot be started, it indicates that it was turned off for compatibility reasons.
2. Use the Windows Security App: Open the Windows Security app by searching for Security in the start menu. Navigate to Virus & threat protection and check if the Real-time protection setting is turned on. If it is off, try toggling it back on.
3. Group Policy Settings: If your device is part of a domain, group policies may be preventing Microsoft Defender Antivirus from starting. You can generate a report using the command GPresult.exe /h gpresult.html to check if any policies are disabling the antivirus.
4. PowerShell Commands: You can also try running the following PowerShell commands as an administrator to reset and re-enable Microsoft Defender Antivirus:
   • To remove any policies that might be set:

          Remove-Item -Path 'HKLM:\SOFTWARE\Policies\Microsoft\Windows Defender' -Force
     

   • To re-enable the antivirus:

          & "${env:ProgramFiles}\Windows Defender\MpCmdRun.exe" -WdEnable
     

5. Update Security Intelligence: Ensure you have the latest security intelligence by running:

      & "${env:ProgramFiles}\Windows Defender\MpCmdRun.exe" -SignatureUpdate -MMPC
   

If these steps do not resolve the issue, consider checking for malware or conflicts with other software that may be affecting Microsoft Defender Antivirus.

References:

• Troubleshoot Microsoft Defender Antivirus while migrating from a non-Microsoft solution
• Ensure Microsoft Defender Antivirus is enabled in the Windows Security app
• Troubleshoot Microsoft Defender Antivirus service startup problems