[Darthtanion]

Ruling out hte power supply or not, it still sounds like a power issue. Either the PSU has a ground or short somewhere or the power source is experiencing some sort of fluctuation. Also keep in mind that if your power supply is not producing enough power for the system, you can also have similar symptoms.

I would not think that it is a cooling problem since these generally lead to a system lock and not a system power down.