How To Fix Microsoft Defender App Log In Error On Windows?

To resolve a Microsoft Defender app login error on Windows, try the following steps:

1. Double-Check Username & Password: Ensure that the email address associated with your Microsoft Account and password entered are correct.

2. Close/Repair App: Press Ctrl+Shift+Esc to open Task Manager. Locate and end the "Microsoft Defender" process. Alternatively, navigate to Settings > Apps > Installed apps, scroll down to "Microsoft Defender," click advanced options, and select 'Repair'.

   If repair fails, choose 'Reset':

   1. With Microsoft Defender highlighted, click the ellipsis (three vertical dots), then 'Advanced Options', and finally 'Reset'.

3. Update Microsoft Defender: In the Microsoft Store, navigate to the Library and check for updates under 'Get updates.'

4. Install Windows Updates: From the search box, enter 'update' and select Settings. Choose 'Windows Update,' and click 'Check for updates' followed by installing any that become available.

5. Perform System Restore: Search for 'create a restore point' and access 'System Properties.' Create a manual restore point if possible; otherwise, use a previously established one or resort to a factory reset using the latest recovery image. Always backup critical data beforehand.

6. Verify Internet Connection: Confirm network connectivity, and potentially attempt reconnection via another router or hotspot.

7. Group Policy Setting: Launch the Group Policy editor (gpedit.msc). Navigate to Computer Configuration\Administrative Templates\Windows Components\Microsoft Defender Antivirus. Check that the policy titled "Turn off Microsoft Defender Antivirus" isn't configured to turn off the service. If it's enabled, switch to 'Not Configured.'

For general login errors, especially on boot, try restarting normally with antivirus/scan services or third-party antiviruses disabled, even if temporarily, until you gain initial login access.

Reference(s):