Yesterday i got a computer i set it up just FINE. I found out it had onboard graphics i had a spare graphics card that fit in the SLOT so i PUT it in and set it up and went to turn the computer on and it would turn on for a second then shut off. So i unplugged the computer and removed the graphics card. However now it won't turn on all it does is turn on for a second and shut off. I have tried unplugging and removing various things. I got it to turn on once when i removed the RAM sticks but it beeped loudly at me because of no ram. So i put them back in and the same thing. Then  i took them out again and then it once again would power on for a second and shut off. So i tried changing the power supply i had two spares that worked last time i checked and after changing the power supply i got the same thing with each one. It would turn on for a second and shut off. However if i leave the power supply unplugged and hit the power button all the fans and such on the motherboard power up and run with no problems. However if i plug the power supply into the motherboard  it will turn on for a second and then off. This problems has me truely stummped and not sure what to do.it sounds LIKE something fried in the motherboard, especially if you've replaced the power supply (which I thought was causing your problems when I started reading your post.  I had a bad power supply making my computer do the turn on/shut off-thing).  There incorrect voltage coming from/going to somewhere.