BleepingComputer.com: What To Check Next

Recently my PSU decided to die. Upon replacing it the computer still dint work so i assumed that the mobo was fried too.

So i decided to put all the parts into another computer to see if it was just the mobo. However when i turn plug in the computer the light on the power supply light comes on, until i try turn on the computer at the front of the PC in which case the PSU turns off and the computer does nothing,

What would this indicate? i unplugged the CD drive and floppy drive to see if that would have any affect but it still does the same thing (appears to have power until i try power it up)

What could this be?

What is the make and model of your computer?

Originally? HP pavillion 720a.

OK incase anyone was reading this also looking for a answer here waht happened

The 12v regulator in the HDD had died. Meaning every time i tried power on the HDD would short out the PSU