Whats stopping windows booting?

ahh basically im fixing a pc for a freind and have gone round and round to the point where my heads spinning! he had some malware a year ago that said "if you dont pay $79 we wont remove the virus and your pc will die" next thing he knows windows wont boot, that was that and he just left it off until now. iv had the hdd out, done all the checks, removed malware, checked file system etc but as soon as you go and put the hdd back in his pc it just goes to "start windows normaly or in safe mode etc" then the pc just restarts and its one big loop. iv done a start up disk and downloaded the 5 bios versions (files contain "flash864" "7vkmls.f4" not sure which to use but tried all) from gigabyte and awdfl882.exe to run each one but each time i try it says it says board number doesnt match?? allso iv tried to do a fresh install on a fresh hdd which fails each time leading me to beleive its bios? or motherboard just happend to go at the same time? any ideas or help would be great thanks