Windows Defender problems

[Benergy]

So while I know Windows Defender isn't the best functioning antivirus program available, I'm a big fan of the 'common senseTM' antivirus that hasn't yet let me down, and it's faaaar more lightweight than free alternatives (I'm traumatised after using the old clunky Avast for years on an XP desktop with less RAM than a modern toaster).

 

Problem:

• The problem began on one of my desktops, and the next day effected my laptop as well (both running Windows 10 Pro with all but one update installed).
• Windows 10 had a popup saying 'Antivirus etc is turned off', so when I open Windows Defender and click 'Start Now', about 1 min later it throws an error 'The service couldn't be started 0x800705b4'.
• When I try to manually start the Defender service in services.msc, it immediately throws an error 'The Windows Defender Service started and then stopped...etc'.
• In my Windows Updates, there is an update that consistently fails (KB2267602 Defender Definitions) while other updates install just fine, this might just be because the Defender service isn't running?
• The problem is exactly the same on the two different computers.

 

Things I've tried:

• Since viruses tend to go after your antivirus first, I decided to install other antivirus to check if there was anything malicious causing this. Both Malwarebytes and Comodo detected nothing untoward on both machines.
• I tried running an 'sfc/scannow'  and 'Dism.exe /Online /Cleanup-Image /RestoreHealth', SFC found errors but was unable to fix them (even in safe mode), DISM ran but there was an error with that too (can't remember what it was but can find out again if you'd like to know).
• Convinced a Windows update broke it, I spent a lot of time deleting update folders and wiping update histories etc. After reinstalling updates and getting everything back as it was, still the only update that didn't install was KB2267602 (it's not installed already by the by).

 

I'm kind of out of ideas other than a full Windows reinstallation (which would be inconvenient as I usually only access the desktop remotely) or *shudder* using some other free antivirus.

Any tips in the right direction would be much appreciated 

[Ex0Thermic]

have you tried doing a system restore back 3 or 4 day ?

also you can try using Tweaking.com Windows Repair Tool 

http://www.majorgeeks.com/files/details/tweaking_com_windows_repair_portable.html

I used this myself to problems on windows lots off time.
it can reset all windows services, which means to with have to go through all off windows 10 pricey settings after running it.

 

also you can try using bitdefender free AV 

it's my favorite antivirus and its very very light on systems resources

http://www.majorgeeks.com/files/details/bitdefender_free_edition.html#screenshots

[Benergy]

9 minutes ago, GeekThief said:

have you tried doing a system restore back 3 or 4 day ?

also you can try using Tweaking.com Windows Repair Tool 

http://www.majorgeeks.com/files/details/tweaking_com_windows_repair_portable.html

I used this myself to problems on windows lots off time.
it can reset all windows services, which means to with have to go through all off windows 10 pricey settings after running it.

 

also you can try using bitdefender free AV 

it's my favorite antivirus and its very very light on systems resources

http://www.majorgeeks.com/files/details/bitdefender_free_edition.html#screenshots

Don't have System Restore turned on, thanks I'll try that tool.

I'll look into Bitdefender if I can't get this working