PC running, but not booting

Last night i walk away from my computer to brush my teeth for a second. I come back and its off. I power it on and it just turns on and won't boot. I thought it was my display buy I checked and everything. only way I can turn it off I'd by turning off the power supply switch. this has happened before, but it was only a display problem.

 

My first guess is the power supply has failed; it's kicking out enough voltage to get the fans spinning and whatnot, but not enough to power up the PC. My second guess is the motherboard has failed, or if you're running an add-in video card, it may have failed. When a PC is running OK, and then just shuts off out of the blue (and it's ALWAYS when we turn our back for a second) and doesn't come back on normally, it's been my experience that it's usually the power supply, motherboard, or video card. There's a chance that maybe the CPU fan wasn't spinning so the PC shut itself off to prevent thermal damage, but the damage may have been done. Or, if the CPU fan is totally dead, the motherboard may be 'sensing' this and preventing the PC from turning on until it's replaced. You can also try unplugging the PC from the wall power socket completely and let it sit undisturbed for awhile; at some point (with the PC still unplugged) hold in the power switch for 10-15 seconds. After maybe 30 minutes or so, try plugging it in and powering up. If it still doesn't power on, it's time to start some deeper diagnostics. When you try to power up the PC, do you get the beep? Are any lights lit up on the PC? Any lights on the keyboard? Does a light come on the keyboard when you press CapsLock or NumLock?

 

alright, its sitting unplugged now. frends said to pop out the CMOS battery. I did that and no luck. well when I push the piwer button it starts fans spin for a second and turns off. second time I press the power it powers on for however long until I switch it off. hopefully its only a power supply failure..

thanks so much so far. also I get no lights on anything.

 

it would be better if you had another power supply to eliminate that problem...i believe you need to take out the battery for about 30 minutes as well, or if you have a jumper to reset the cmos, it will do the same thing.

 

ok just plugged the computer in and tried turning it on and the same thing is happening. Ive taken out the battery and ill let it rest for a half hour and how it goes. I have a spare power supply I'll try right after.

 

just tried everything and no luck. the computer still powers on for 1 second and turns off. the second time I press power it turns on until I flip the power supply switch. the motherboard is only less than 2 years old so it would suck if its that. is there another way I can check if the motherboard is dead? I can try another graphics card and see if that's the problem. any more advice would be amazing.