Re: Motherboard or Power supply?
It could be the PSU open your case and check if any lights on the mobo are on if not id say the PSU is dead. Here is what id do:
step 1. unplug the pc
step 2. take case off
step 3. unplug everything except the 20/24 pin power cord , the 4 pin cord, 1 stick of ram and leave the graphics card in.
step 4. plug the pc back in and see if it starts , if not, remove graphics card and ram try again. If still nothing and no lights on the motherboard i think the PSU is dead.
step 5. lend a PSU if possible or buy a cheap and nasty one to test with.
that's just what I would do unless you no nothing about computers and too scared to break anything take it to a computer shop.