I was working on one of my friends computer, an old hp pavilion and it won't turn back on. im guessing all i have to do is reset the mobo but im not sure where the switch is or if there even is one for that matter. the power supply starts up for a second, fans go and such but then it cuts off. i know it's not the power supply or chord because i tried two others and same result. sry i don't have the exact model but could anyone help me with this?

Sounds like somethin's shortin. If you installed a new mobo recently, you may have put a riser in the wrong place. I hope you didnt force the CPU into the socket. That will wreck it. If it wont go it, turn it around till it goes in. You really need to provide us with more infirmation of what you dod. Did you move the risers when you installed the new mobo at all?

I don't know where you read that he changed the mobo. he only installed another PSU, not a new mobo.

I had the same exact problem with and old HP Pavilion. It just started to happen all of a sudden and got progressively worse with time. I replaced the stock 150W PSU with a 180W PSU, that fixed it for a while but then problem soon returned. I was only able to turn it back on after unplugging it for about a half hour or so, it would stay on, but if i turned it off it and tried to turn it back on, it would do the same thing as yours... it would spin up for a second then turn back off.

I tried everything I could think of and finally gave up. It was a piece of crap celeron 400MHz anyways, I wouldn't have had a use for it, but my sister wanted it. I just wanted to let you know that your problem is not unique, I think it's just the rubbish parts that HP uses in their systems

sorry about being somewhat vague of what i did, i was in somewhat of a hurry lol. to answer some questions though, no i did not install a new mobo, dk where that one came from, and still have not gotten it to work. im going to try unpluging all the devices again and see if that works. more then likely though, the mobo or something shorted out and i'll have to go buy a new computer. your right though, it is a peice lol. thanks for all your help