Problem

Hi i have a problem

My PC Shuts down completly literally random.. at any time, like imagine turning off the power, that kinda shut down

now i cant switch back on till ive turned the back switch off, and had it off for a few seconds then press the power button

i think either my power supply is messed or motherboard

If you've got a pre-built machine like Dell or whatever, I'd put my money on a failing power supply.  It's the most common thing I have to deal with at work.  Get yourself a nice Antec PSU.