Windows Defender not starting after update

[Moonsurface]

I did the major 1511 update last night and now Windows defender won't start. I can try to switch it on but it turns itself off. I keep getting notifications about not having virus protection.

I have Malwarebytes installed but that never caused a problem before. All updates have been done.

Settings screen options for defender are greyed out. What do I do now?

 

[Moonsurface]

For now I've fixed this by installing AVAST (which does seem pretty good tbh) however I would like to know why defender wasn't starting before. I didn't have any other AV installed, except malwarebytes and that never caused a problem before.

 

[Moonsurface]

Anyone?

 

[leeshor]

The AV software I install disables Defender by default. But I don't feel that's your problem. Any strange stuff in your Windows logs.

 

[Moonsurface]

My SP3 has been giving me noticeably shorter battery life lately about 4 hours compared to 5-6. Which logs do you mean? The reliability ones?

 

[GreyFox7]

Try uninstalling the other software even though Malwarebytes will normally work alongside it sounds as though during setup Win 10 detected other antivirus and disabled Defender. It's confused.

Otherwise there may be some Powershell command puffery in your future ... or a Reset