What should I do after someone had unauthorized physical access to my PC?

Episode 1218 (1:11:15)

Elizabeth from Santa Clarita, CA

Elizabeth wants to undo whatever her nephew did to her PC after he came to visit. He's got mad computer skills and she caught him rummaging around her computer without her permission. Leo recommends backing up her data, formatting the hard drive and reinstalling Windows from a known good source. That way any modifications he's made will be wiped out.