computer will not work with new cpu

I have an HP Pavilion a1473w desktop, which came with a P4 2.8 GHz cpu. The specs on the mb, which is an RC410-M (Asterope), with an ATI X200 chipset, says that it will support, among others, a Pentium D 9XX series (Presler) cpu. I bought a Pentium D 945 3.4 GHz cpu, with Intel heatsink, and installed it on the computer. But after the computer starts up, it shuts down in about 5 secs. After being told numerous times by the tech “experts” at HP that the computer would run this cpu, I went ahead and bought it. But I tried to install it twice, and both times the comp would not work with it. Does anyone have any suggestions here?

Mike
ps. I also installed a Vision Tek x1550 PCIe card. Would this make any difference?