Windows Defender problem
Do you have any antivirus installed in your PC? If not, what was your previous antivirus and how did you remove it?
Did Defender detect anything in recent history? How often do Defender turns itself off (I mean right after turning it on, after a restart, after few days, etc.)? Do Defender present any error while turning off? If so, please give us that error code/message.
Please mark replies as helpful/answer if they are.