Windows Defender won't start on Windows 8.1

2

I'm currently using Malwarebytes Pro but want to have Windows Defender on as well since MAMB isn't really an antivirus. They're supposed to be compatible but for some reason I can't turn on Windows Defender; I see the message "Your PC isn't being monitored because the app's service stopped. You should restart it now." When I visit the process list, I see that WinDefend is in the "Stopped" state, and when I turn it on it flashed on for less than a second before going back to "Stopped".

I've uninstalled Malwarebytes and removed anything related to it I can find (ProgramData, registry entries, etc.) but I still can't turn on Defender and get a timeout error any time I try to enable it. I've never tried to install any other antivirus so it's not possible that any remnants are conflicting. Additionally, Windows Update fails to install any Defender-related updates.

What can I do? I know I could just get a different AV but I'd like to get this working.

Matt

Posted 2014-10-07T17:16:20.973

Reputation: 235

Your inability to launch Windows Defender has nothing to do with Malwarebytes. This sounds like system corruption use DISM and sfc to confirm. – Ramhound – 2014-10-07T17:30:36.273

Answers

1

You should probably run System File Checker:

sfc /scannow

This will go through and make sure your Windows install is good, including Defender. If this doesn't resolve the issue, please check back with details regarding any errors reported in the system logs.

music2myear

Posted 2014-10-07T17:16:20.973

Reputation: 34 957

Should've thought of that; it found corrupted files and managed to fix some of them, Defender now works. – Matt – 2014-10-07T18:47:26.787

Cool. I'm happy it worked for you. – music2myear – 2014-10-07T19:25:40.127

Asked: 2014-10-07T17:16:20.973

Viewed: 6 432 times

Active: 2014-10-07T17:29:58.390