Which antivirus program are you using as this can be caused by malware ?
If you don't have MBAM installed then you can download the free version and run a scan with that.
https://www.malwarebytes.com/mwb-download/In Settings/My Account you can end the Premium free trial which will stop the pop ups.
You can try the File Associations fix in the Windows Repair program after you have run a scan with MBAM, as the program can't repair infection damage while the infection is still present.
If the program can't fix then I'll ask one of the admins to have a look at your problem.