Compaq Problem

Someone gave me a Compact Presario with windows xp. It's about a year old. I reformatted the hd and got the hd up on another computer. I reinstalled the hd in the compact. When I turn the compact on the power supply and fans come on. It clicks and goes off.
I looked at the mother board and don't see any signs of damage.
I checked and it was doing the same thing before the person gave it to me. Any Ideas?