HP a320n fan spins on then turns off

[mobo248]

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.

 

[Nodsu]

You have a short somewhere and the PSU turns off to save itself?

Unplug everything. Then try powering on only the PSU; PSU and the motherboard; PSU, motherboard and RAM etc.

 

[mobo248]

Thanks for your input, after unplugging everything as suggested I found that the issue was with the power button. When I pressed it in, the button remained depressed and caused the computer to power off. Thanks again..