Windows Defender will not turn ON

[System]

Windows Defender unable to turn On.


I recently had Avast antivirus installed, just for an additional scan. But removed it properly using Revo Uninstaller.

I ran Services.msc and found that Windows Defender is set to manual (but is unable to be set to automatic, location is greyed).

When I run Action Center, in order to Turn ON Windows Defender it simply opens Windows/System32.


Found the following while researching online,

Performing miscellaneous checks:
* Windows Defender Disabled
[HKLMSOFTWAREMicrosoftWindows Defender] "DisableAntiSpyware" = dword:00000001

Unable to set to '0', displays an error message..
"Cannot edit DisableAntiSpyware"


Please help.

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