Shut down on startup

[RandomName]

Yesterday I was using my PC no problem. But this morning I powered it up, it booted to a windows home screen and shut down after a couple of seconds. I true to power it up again but it would shut down emideatly. I try tested the power supply useing the paper clip trick, and it works. Tried inpluging each stick of ram independently, no result. Tried booting up with ou the gpu still shuts down. What should I do? Please don't tell me it's the mobo.

[Uwillparish]

Specs?