This sounds like a virus to me. A hijacker. A virus that's taken your User Rights and modified them so you can't access the virus. I sometimes use the processes that BLEEPING COMPUTER offers.
I don't suppose you've created a 2nd UserID somewhere in the past, have you? Like the Administrator account and that you also know that account's password?
Sometimes, I've cured viruses by logging in as that 2nd user (as long as it's got Administrator rights) and found viruses that 'my ID' couldn't locate.