Or both.

The power supply can go flaky on the 3v or 5v and still run the fans and spin the drives with the 12v rail.

On the motherboard look for anything looking fried and bulged or leaking capacitors especially around the voltage regulator section and near the video card slot.

If the mother board is fried like this don't replace it without checking the power supply as a bad power supply can cause this type of motherboard failure and you don't need to do it twice.


UncleVom