I'm trying to repair a friend's Dell Inspiron 620. It has Windows 7 Home Premium (x32), and we'd like to install Windows 8.1, if possible. However, no matter what I do, it gets stuck in the middle of loading. I've tried using the built-in startup repair, booting into safe mode, booting into a Win7 iso running on a flash drive, and booting into the Win8.1 DVD. They all stall mid-load, usually on the black screen with the Windows logo. The spinning icon or the animated bar freeze. When trying to boot into Safe Mode, it stalls on "classpnp.sys"
I've run hard drive and memory tests, both with the internal diagnostic tools, and DOS-based ones via flash drive. I've also blown out the case with compressed air.
I've completely run out of ideas.