E-Machine T2558 quit booting

[PoonDoggy]

Client says he turned unit off and now it wont boot up. I have changed psu to Antec 500 watt Smart Power 2.0 and the fans will turn if you dont push the power connector all the way in and hold the connector in just the right spot. I have tried a known working Premier 300 watt psu and can plug it in all the way and the cpu and psu fans spin, but cannot hear the HDD spin up. I get nothing but a black screen on monitor, no POST or anything. I have tried a known working PCI ATI graphics card and still get the black screen <of death? >

I am inclined to diagnose as a dead MoBo. But, would like you opinions.

E-Machine T2558
2.8 Celly
XP Home
Intel Extreme Graphics integrated 64MB
80 GB HDD
512 MB PC2700
Intel 845GV Chipset

Thanks

[bwcc]

If you pull the memory or videocard and there are no audio beeps (assuming it has an internal speaker), then yes, I would concur with that diagnosis.