There are several possibilities. A power supply would be the most unlikely since there are 4 power supplies. It would be incredibly rare to have 4 bad power supplies. It could also be the power distribution board, interposer card(Card that the Power3 connector attaches to), one of the devices attached to the the interposer, the system board, or an external power issue.
I would suggest disconnecting the CD-ROM and anything else connected to the interposer. If that does not resolve anything then try another power outlet and bypass any surge protectors or other devices between the server and outlet. You can also clear the NVram via jumper on the system board. If there is no change then you will have to randomly start replacing components to try to find the faulty component.
Thanks