PC powers on for 1 second then shuts off

[Gazza1]

why does my computer do this sometimes?  The only way to fix it is unplugging the PSU for a few min then trying again.  I've tried different psus, all high quality, so it must be the mobo?  But it does it on a couple of my computers.  What's the deal

[daclayman]

You need to clarify: upgraded PSUs on all/some computers? Same problem on all computers with same/different power supplies? To solve an issue, it has to be isolated.

[Gator-hex]

I have this with one of my power old supplies, one of the power rails seems to be dead, and I can only run half the watts on the 12v rail. But it could be you just wired something up wrong, if you plug in a speaker on the motherboard it might beep an error code if it's a motherboard error, if not you can get a motherboard diagnostic board off ebay.