my video card works fine when i put it in the motherboard, but once i screw it in the bios doesn't post (one long beep, two short beeps) and the video stops working. i assume this has to do with a grounding issue but i have no idea how to resolve it or what might be wrong. the motherboard is properly mounted with washers in the screws. it's a geforce 9800gt, although i don't think it matters.
Screwing it down may flex it slightly, bringing it in contact with your mobo or a component on it. If you cannot see an obvious cause, try running a line of electrical tape along the back edge of your mobo and see if that solves the problem.
Worst case, it is your mobo that is flexing slightly, and it has one or more cracked traces or bad solder joints (esp. on the PCIE connector).
i tried unscrewing some of the motherboard screws and i took out 4 to resolve the problem, but i can't pinpoint the exact location. i guess it might be, as you said, the cracked traces/bad solder joints.. i'll look into it later when i get home
are the mounts on the video card at 90 degree angles? Perhaps when screwing it in it is rocking the card in its slot enough to lose contact. Or maybe a piece of something is in the slot preventing it from seating all of the way.