I have a Dell Demension 5100 that won't power on. I have disconnected all hard drives, cd rom, and diskette drives. Still won't power up. There is a led on the

motherboard that lights up when the power cord is plugged in but nothing else happens when I hit the power on button. I think the power supply is the problem

but is there anything else I can try to make sure that its the power supply and not something else!!!!!!!