Why do I keep hitting a blue screen?

So I got a quicksilver from a pawn shop for 10 bucks. It was cheap and I tested it before I bought it. When I got it, it had graphical issues (lines through the screen and such) and didn't boot to the OS. I got it home and attempted to get it running. First thing I did was replace the graphics card which fixed the graphical errors. I then tried getting into the OS. I found that the drive that had the OS installed on it was corrupt and failing. I replaced that, and got my hands on a OS 10.5 retail install disk. It doesn't matter what I do the retail disk will not get past just a blue screen and mouse. I put it in a different machine and used that machine to install OS 10.5 onto the hard drive (the machine has a 1.5 ghz aftermarket proc from OWC so I installed it to an apple file system partition rather than a EUID partition) normal boot hits the same blue screen, install CD blue screen as well, safeboot actually comes up to the OS. Anyone got any ideas what the heck is going on?