|First I would download the MalwareBytes freebie file on another computer then Install it "from a flash drive" on the dud computer. If it finds anything when run, let it remove it then get its data base updated then run it again. If it won't run then change it's exe to either cmd or bat (which applies to both the download and the mbam.exe program file).|
I wouldn't rush into re-install without exploring other avenues first. After you have run MalwareBytes there is always the System Restore option.
If you can download it, this program will unearth the product key stored on the hard disk:
You should obviously get this before re-install or it will be lost.
Can't help wondering why no Anti-Virus when there are at least three freebies around:
"Avast", "Microsoft Security Essentials", "AVG" - arguably in preferred order. Prevention is always better than cure.
Always pop back and let us know the outcome - thanks