My Computer won't start, possibly PSU?

[Minfante25]

Hey I am ok with computers and understand alot but there r some things i dont get so i will explain my situation as dumb as i can. I come home one night and my computer was shut down without me shutting it down. So i go to power it on and it doesnt turn on. So the first thing i tried was to switch the psu from on to off then back again and the computer booted (without me pressing the power switch). However after lets say 12 seconds it shut down again. So i tried the switching thing again and it worked but shut down again. after the third try the computer booted and was workign fine. I come home from work and the computer won't turn on and this time switching my psu on and off won't work anymore. I think its the PSU but i am not sure bc when i put the switch to the on position i get a green light on my motherboard but the computer still won't start. Please help, any help at all is greatly appreciated.

[Chrysamere]

it could be your video card, i had a radeon x1950 pro running on a 300 watt psu, same **** happened couldnt turn it on after a year, replaced psu with 500 watt, new mobo, new CPU, it only worked without vid card. the video card overheated and now it cuases a short everytime its inserted make sure u check the vid card at ur friends

[Minfante25]

I tried unplugging my Video card and it still didn't start but I am not sure if you need a video card to get a boot up.

[ctm2k]

Sounds like a bad board or cpu

[Peter.Cort]

try running a new psu. it could have just crapped out which would why it would have started up but only for a few seconds.