And it gets more interesting.
I pull the case, and swap HDs. I notice that the CPU fan (~3 month old Intel unit that came with the CPU) is acting like a retard on ridilin. It sort of moves, but never spins up.
I try loading with the new HD and get the same issue. On a fresh HD.
Can it be that the mobo is sensing that the fan is not working properly, and shutting everything down?