I was meaning to get this plea for help up sooner but got engrossed in my 40K photo thread, and oops, now I only have 15 minutes left...

My home computer died on me last night, my roommate believes he knows the problem but second opinions always help... What happened;

My computer was on and running fine, I went upstairs, came back down and as I was pulling up my chair, the PC rebooted, then while it started back up, before the CMOS and ramcheck came up, it turned completely off. Hitting the power button does nothing, but if I turn off the power supply and turn it back on, it will again start up for 1-3 seconds then conk off before the ramcheck pulls up. I've done the whole unplug and completely turn off, leave it for a time, and then retry route, same effect.

While the power supply switch is on, the lighting from some USB cables and other LEDs are illuminated, and the fans spin when it does its attempt to start.

My roommate believes it is either the Motherboard or the Power Supply, and is favoring power supply as the problem because he claims that if it were the motherboard, it would just continue to sit there dead-screen, but the power wouldn't turn off.

Does anyone have any alternate possibilities it could be, or can confirm his diagnosis. I leave in 15-20 minutes for lunch and plan to run out to get a new power unit, but would like to know if it may be futile or the right move.

Unless you're really good with computers I think you should let someone professional look at it.