I have a HP a320n, at first the when I plug in the power. The green light on the power supply turns on, the power supply fan spins and the system fan spins for about 2-3 seconds and then turns off. If I press the On/Off but on the computer, nothing happens. The fans only spin if I unplug and plug the power back in. I've tried swapping in a new PSU, but still the same thing occurs, any suggestions on what can be wrong. Your input is greatly appreciated, thanks.