My son gave me an old games pc of his which has a really fast processor and had all the crap taken off so it was pretty clean program wise when I got it. It is for my grandson so he can use a big dell touchscreen monitor. DS installed a hooky win 7 downloaded from utorrent. At first it was fine but I think microsoft virused it when it downloaded updates. 
Anyway it went crazy...giant lettering, weird shapes and outlines and colours..a disaster! Despite hours trying to uninstall this copy, initially from the control panel then going into the computer OS (C) drive and looking for all the microsoft.NET etc stuff and even uninstalling all the updates, which the PC promptly reinstalled when I restarted it
So I bought a genuine windows 8 with activation code thinking it would partition the win 7 and work fine. But it cant install because the underlying files are corrupt. I tried custom install and opted to partition, no luck ditto with the straight install. Trying all day with no success. I have a major headache and have run out of ideas. Any thoughts before I take it back to DS and get him to wipe the hard drive for me. btw. there are NO files etc to save, nothing to backup. We only used cbeebies website and another kiddie site.