"...12V@15A..." This could be the reason. Try a better P.S. with 18A. or more to 12v. rail. Also 20A. to 3.3v. rail is poor. What CPU is installed ?
Well, I went for overkill and got a Antec 500w PSU
+3.3V@32A, +5V@35A, +12V1@17A, +12V2@19A, -12V@0.3A
But my issues are still the same, the PC starts up, CD-ROM works, CPU Fan works, but no joy with the Monitor. Tried both onboard Video and a working Video card.
Any further suggestions or comments will be greatly appreciated!