I work for an onsite technician company, so, I had a customer yesterday evening whose computer would not power on.
When I arrived it was as described, press the power button and nothing happens. The PSU had a faint green blinking light on the back but did not apppear to idle when the power button was pressed, nor did it power any of the components.
I replaced it with a power supply I bought on the way there. Afterwards, the power button gave power to the supply (and the front LED case light worked) and everything in the machine booted except the processor fan did not spin at all, and the boot process never began on screen.
I am wondering, would the motherboard or CPU be dead? I am thinking the P4 plug on that PSU might be a piece of crap too, so I will try a molex to P4 adapter.
I believe this was a 600W PSU and this is a 7 year old HP media center so its more than ample.