Probably PSU related issue, any ideas?

Ok this is from a third party that I'm trying to solve, tbh I'm thinking it's not actually a problem at all, but if it is it sounds psu / 5v related, so this is the best place of any I know to ask about any PSU stuff :) Quote of the "problem":



Specs:

Fujitsu P420 Desktop prebuilt genericness, brand new.

PSU D12-250P1A

Mobo: Fujitsu D3230

Bios: AMI Aptio 4.6

Other specs in data sheet @ http://ift.tt/1ulscKt

Quote:

when I plug my computer into the wall socket then switch the socket on, the computer's hardrive light, on/off button light and fan briefly come on then go off a second or two later. This all happens even though I have not touched the computer on button at all. The computer is then in a off state.

From what I can tell so far, everything else is fine. I'm gonna make a quick guess as a bios setting, psu "setting", or at worse a wire stuck the wrong way round? That's if it's not just completely normal.

Probably PSU related issue, any ideas?