I had a problem on a non-corporate device the other week with Defender failing to start, if you try to start the antiviral solution, it would crash it also appeared that Defender was not correctly loading it drivers as it should be.
If you try to start the Defender interface, it would either crash or fail to appear on your screen, you really need to look at the logs for this issue, but for general advice you can try the steps below.
This particular laptop had all the latest updates installed, and it had been rebooted multiple times in the usual Windows fashion.
The Internet can sometimes be a very unhelpful place when you have a generic problem that will ultimately take you down lots of rabbit holes and eventually lead to reinstall Windows.
I would suggest before you hit the big red button to rebuild you give this go:
- Click Start
- Type “powershell”
- Locate the Powershell icon
- Right click the Powershell icon
- Choose run as administrator
- Enter this : Get-AppxPackage Microsoft.SecHealthUI -AllUsers | Reset-AppxPackage
- Wait for the command to complete
- You may be asked to restart Windows if prompted, if you are prompted, ensure you restart Windows
You will then notice once Windows has restarted Defender should now operate normally as it’s been reset back to its original settings.
If this method does not work then you can try this as well:
- Go to C:\Windows\System32\SecurityHealth if you notice that this folder is empty this could also be a problem and will need to be fixed.
- If the folder is empty you will need to download a file from Microsoft here
- Right click on SecurityHealthSetup.exe and choose Run as administrator (elevated mode)
- When run you should then notice the UI for Defender should start behaving as normal
- You may need to restart the computer for the changes to take effect.
If you find yourself getting an error that mentions the access denied, you did not run your Powershell prompt elevated, follow the instructions again but correctly follow them this time.