Computer displaying no image!!

[delusion_2005]

My friend has a 9700Pro, with a P4 478 2.8Ghz, some how he left his conputer for the whole day and when he came back there was no image displaying oh his monitor, he took it to the computer shop and they said it was the mobo, so he got a new mobo, he took it home and chuck in the 9700 Pro and still won't no image, so he decided to try the card in another friend computer but the cards works there, he took it to the computer shop again he tried another 3 graphic 1 of 3 of them work and displayed an image, the card that works was a Ge force 4 mx 4000 64mb. So what the heck is wrong with his computer, i believe its the PSU dying am i correct?