Solved. I could only boot via PSU straight to BIOS with a clean CMOS.
I had no case (at that time, due to mounting and remounting CPUs till I was grey in the face from TIM). Once the case was there and there is a power button wire hooked to the Power, Reset and HDD light panel-of-pins, then you can let it boot silently to the 2 green lights (on a full unplug of the PSU) and then hit the power button and it just boots, np.
So the solution is to case the board or add a power button wire hooked up to the MB.