I want to turn on windows defender on my windows 8.1 but when i click, it display "An error has occured in the program during initalization. if this problem continues, please contact your system administrator

Error code: 0x80070002

What should I do?

Do you have any other Anti-Virus software installed?

Since when this problem started?

Here is a registry key fix:

https://www.sophos.com/en-us/support/knowledgebase/121342.aspx

Please remember to backup the registry before doing any change to it.

-Jeff