Nope, no blue screens, and I have not overclocked this machine. As far as new software, I don't believe that I installed anything new that would cause such a problem. The HD does not spin at all (or at least very little) when the screen goes black, though the HD stays on steady.

At this point, I am unable to tell if I have an overheating problem, since the system won't start up at all...even to do a system restore.