So, you might want to try the jumper method of powering on both PSU's with nothing attached. Don't leave them powered on if they start, that has the potential of damaging them. If they power up, but will not when connected to the mainboard, take out the CMOS battery on the board, unplug power to the PSU, and press and hold power button for about 30 seconds. Or, if your mainboard has the option, clear CMOS. This is just grasping at straws, but occasionally I have seen boards that wouldn't power up otherwise, as a means of preventing damage from the fault that exists.