Complete change of ownership of a computer is about the one case in which I would recommend, and have done, "wipe the disk and reinstall Windows".
As a bonus, that gets rid of all Fred Smith's viruses, and all Fred Smith's illegal kiddie porn, and no doubt other stuff that neither of us has even thought of.
recommended.
\It only takes a minute (and by minute, I mean two hours) but the piece of mind earned (as well as added reliability, speed) is priceless.
How much time has he wasted with "Fred Smith" that could have been better spent?