Windows Defender won’t open or isn’t working properly, which could mean you can’t edit settings in Windows Security, or malware is running wild on your system because you don’t have the right protection. Below are several reasons why Windows Defender won’t open and how to get it working again.

Here are some examples of situations where Microsoft's anti-malware app will not open or will not work properly:

There are several things you can try, but follow this list in the order it is presented so you can try the easier solutions first:

Restart your computer. This is a common first step in troubleshooting Windows issues, and it may be all you need to do to get Windows Defender working again.