If your puter is running a P4 2.8 H/T with a 800 FSB your MB is a socket 775 which supports PCIexpress16x1. I googled your video card & it supposedly supports AGP & PCIEx16. Have you switched over from onboard video to add on video card in your BIOS? Tried reseating your card & if your card has a PS connection is it connected? Have you downloaded current drivers for your card?
Looking at the motherboard and doing a diagnostic shows it only has an AGP slot unfortfunantly. My videocard is an nvidia 5200 PCI. I can't sit that in an AGP slot can I? Its in a PCI slot right now. The BIOS settings should all be correct it automatically goes for the AGP and if no AGP then it goes to the PCI slot and I keep the ATI graphics card(the noboard crappy one) disabled. Not sure about the Power Supply connection I would definantly have to check that out. What would happen if it was not hooked up? There is one odd thing I have noticed.
The fan on the videocard has not been spinning I don't thionk and it may have started recently. Also When I run RivaTuner and use its hardwqare monitoring it says my core clock GPU is running at 100 mhz when it should be running at 250 mhz, but when I run another nvidia diagnostic program it says the clock is rnning at 250 so I really don't know which one is correct. If it is only running at 100 that would be my problem
See the thing is I used to run WOW on a computer that had less ram, same vid card, and a lesser than CPU. I thought this computer would run it no prob but it can't. Anytime I run a game like WOW it just keeps pausing / freezing evey 3-4 seconds. One time I screwed around with some forceware hardwrae lvl settings on my vid card and I actually got WOW to run smoothly for a little while but since than it has stopped. I dont understand half of those rlly complicated directx / open GL hard ware level video settings you find in the rivatuner / special nvidea programs so I don't really knowq what to set. I try to optimize it for performance as best as I can.