Hi Liam,

You seem to have an issue with running Windows Defender on your PC. Can you please let me know some of the things like:

1. Did you use any other 3rd party antivirus application on your computer?
2. Are you administrator of the computer?

Some 3rd party antivirus programs may turn off Windows Defender when they are installed to be used instead, and will not allow Windows Defender to be turned back on until the 3rd party antivirus has been uninstalled or disabled.

You can refer to these steps to turn on Windows Defender:

1. Press Windows and X keys together.
2. Open the Control Panel (icons view), and click/tap on the Windows Defender icon.
3. In Windows Defender, click/tap on the Settings tab, Administrators in left pane, uncheck the Turn on Windows Defender box, and on Save Changes.

If the issue still persists, try to perform a system restore to earlier date (probably 3 days) check if that helps.

• Press ‘Windows Key + R key’
• In the run window type ‘rstrui.exe’ and click on OK
• Click on next in the System Restore window.
• Now choose the restore point of your choice, and try to restore your computer back to earlier state.

I hope this helps.

Regards,
Lokesh