I need help fixing a friends computer that I am constantly having to fix.

My buddy has a custom built gaming rig. He has an intel quad core, 4 gigs of ram, vista 32 bit (I know 32 bit doesn’t allow full performance which is why I’m trying to boot onto my windows 7 64 bit disk) and an sli compatable graphics card with 1024 mb of ram. I can’t exactly be more specific because his computer won’t even boot without this error popping up. Which is wierd because It was just working perfectly fine just after fixing it a couple days before. It was freezing everytime he tried to play a game for 20 minutes or so, and it could hardly boot then either. When I finally got it to boot, it went onto his desktop. I installed the latest video card driver which he had the very first driver that came out for it. I then installed all the windows vista updates. It was running fine till that error. I told him to insert his vista 32 bit disk to try and boot into a system repair. However everytime he tried doing so, he gets this error. I even tried inserting my windows 7 64 bit home premium disk so that i could just install the os over his crappy one. However I still got that same error. What could be going on? If you need more information, I’ll do the best i can. Thank you!