A friend's machine recently died. At first I thought it would be the power supply but now it appears the (green) light on the front of the machine is lit and the motherboard light is also on. When an attempt is made to power on the machine there is no feedback, such as a couple of beeps. I now believe it's more likely to be the motherboard than the power supply. Based on these symptoms, what's your diagnosis? I can temporarily replace the psu with one of my own if there is any ambiguity in the likely cause of the problem to ensure whether the psu is to blame.
EDIT: I connected the motherboard plug from my machine to the machine in question. The difference this time round booting it is, is the fan turns on (and the fan on my machine..). There's no output to the monitor but I guess this could be due to my machine being only 350watt and the other 400watt. There is a four pin plug connected on the other motherboard. Connecting my plug to it turns the machine unresponsive (as opposed to the fan turning on when only my mobo connector is connected to it).
So, guessing it is prob the PSU...?