Your first step should be to be sure what you can't lose is on your backups (yes, that's PLURAL!)
With that out of the way, try all the tools and scans Grif notes at the next link.
Someone downloaded ilivid,now can't start Windows unless I use recovery. When windows starts and I delete ilivid, and run Malwarebytes, and Superantispyware,and it finds a few items, deletes them, and tells me to restart. When I restart, the whole process starts over again,need to restore to earlier time again and all is back.