My inclination (as hinted above) would be to plug in a different hard drive and see what it does. I have an old clunker 40GB IDE that I keep for such exploits.
It may need to have an operating system installed on it, but if the BSOD recurs after that, you know you're down to Mobo or CPU. I've never had a Mogo or a CPU die on me. I've had lots of hard drives pop their clogs (well, three of them, anyway).