Microsoft Defender Windows Application will not open

Question

Microsoft Defender will not open. When I click to open it shows the loading blue circle then does nothing and never opens. I have tried uninstalling and reinstalling the app and restarting my computer, but it has not changed.

Answer 1

Hi, I'm Bernard. I'm happy to help!

This happens when there is a corrupted file in the Windows Defender folder or a reconfiguration is needed. First, you need to check if you have a work or school account:

Open Settings> Click Accounts> Click Access work or school, then disconnect the account there. If there is no account, or it is already disconnected and you have the same issue, follow the steps below:

Note: Before doing the steps, I suggest completely uninstalling the third-party antivirus first.

Method 1. Repair Windows apps and Windows Defender:

Open Terminal (Admin) or Windows PowerShell(Admin) (Press Windows key + X then click Terminal(Admin))

Copy, paste, and enter the command below:

Get-AppXPackage | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"}

Restart the PC and check

Method 2. Reinstall Windows Defender

Open the Registry, then go to

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender

Then delete the Windows Defender folder, restart the PC, and recheck it.

Answer 2

Since uninstalling/reinstalling the Microsoft Defender app and restarting did not help, use this troubleshooting path:

1. Check whether the Defender services are running. Open PowerShell as administrator and run:

      Get-Service WinDefend, WdBoot, WdFilter, WdNisSvc, WdNisDrv, SecurityHealthService, wscsvc | Format-Table -Auto DisplayName, Name, StartType, Status
   

   Expected results include:
   • WinDefend = Automatic, Running
   • SecurityHealthService = Manual, Running
   • wscsvc = Automatic, Running
   • WdFilter = Boot, Running
   • WdBoot being Stopped after boot is normal
2. Review Defender event logs. Open Event Viewer and go to: Applications and Services Logs > Microsoft > Windows > Windows Defender > Operational Check for these events:
   • Event 5007: Defender configuration changed
   • Event 5001: Real-time protection was disabled
3. Rule out interference from other antivirus software. If Microsoft Defender Antivirus is intended to be the primary antivirus, uninstall any non-Microsoft antivirus software.
4. Run Microsoft Safety Scanner to rule out malware.
5. Reset Defender definitions and platform. Open Command Prompt as administrator and run:

      MpCmdRun.exe -RemoveDefinitions -All
      MpCmdRun.exe -ResetPlatform
   

6. Back up and remove Defender policies. Warning: this removes Microsoft Defender Antivirus policy settings from the local machine. In PowerShell as administrator, back up the policies:

      New-Item -Path "C:\DefenderTemp" -ItemType Directory; Invoke-Command {reg export 'HKLM\SOFTWARE\Policies\Microsoft\Windows Defender' C:\DefenderTemp\_DefenderAVBackup.reg}
   

   Then remove the policies:

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

7. Run Microsoft Update, then verify Tamper Protection is enabled.

For the Microsoft Defender app itself on Windows, installation alone does not activate it. The app must be signed in with the Microsoft account used for Microsoft 365. If the app is uninstalled, it is not automatically reinstalled and must be installed again manually from the Store.

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References:

• Troubleshoot Microsoft Defender Antivirus service startup problems
• Troubleshoot Microsoft Defender Antivirus while migrating from a non-Microsoft solution
• Windows