Nah, nothings overheating. It's not overclocked or anything. Plus I could leave it off all night (too get cool), then boot it up, shut it down and try and turn it back on and it does the same thing.
I've already ruled out overheating, I'm still thinking its either the PSU or just a bad motherboard. The Nvidia RAID controller was dead on arrival, so I think its safe to assume it could have other problems. I just didn't feel like RMAing it, because I don't use RAID anyway.
Does anyone know for-sure what the flashing yellow light is? It's located at the very south-west corner, near that display thing with the two digits, and the three start-up indicator lights.