My old power supply died so I had to get a new one and I installed a Dark Power Pro 10 1200W. I wired everything but when I plugged the power cable all of the fens went on, everything looked like the pc is on and then it went completely off. The little light on the motherboard is on. When I unplug the power cable and wait for the light to go off and plug it in again same thing happens.
I tried the paper clip trick and it is pretty much the same. It goes on for a sec and then off again.
I tried unplugging the ram, HDDs, Video card, CPU... nothing. When this happens while everything is plugged in all of the fans start working.
Well if it fails the paper clip trick then there's clearly something wrong with the power supply. Same thing happened in my computer build, fans would spin for a few seconds and everything looks like it's working fine, then the fans will stop spinning and nothing happens. Swapped out the power supplies AND tested it with a voltmeter; confirmed dead twofold. Also tried the paper clip trick, and passed it, but that doesn't always mean the power supply is working correctly.