no audio/video after new video card install

Hey guys, I'm hoping one of you can help me!!

First of all, I have a Dell Dimension XPS Pentium 4 3.4 GHz, 3.39 GHz, 2.25 GB RAM. I run XP Home

My story of pain and frustration began when I upgraded my video card from an Nvidia 6800 to a 500 MB RAM Nvidia 8600. This happened quite a while back, late January I think it was. Although not the most technical person, I installed it myself and am almost positive I didn't ruin anything by installing it. Stupid me forgot to uninstall the previous nvidia drivers, so upon booting up my system, I ran into the bsod, rambling about bios. Upon a call to tech support, I booted into safe mood and took care of the problem.

All seemed to go well, until the next day. After starting up, I began to notice that video across the board is choppy and unwatchable. This applies to computer games (the reason I got that dreaded video card in the first place) and anything in media player, from downloaded tv shows to my own dvds. To coincide with the bad video, all audio, from cds to game sound effects, to the windows start up jingle, is gone. I can run applications (like mozilla) fine. 3 tech guys and about 8 hrs of my life later, the problem was miraculously cured. This was beginning of February.

It is now June and I just moved. Upon booting up at my new place, the problem is back. Choppy video and no audio. I don't really want to call tech support back, as I don't want to block out a 3 hr chunk of time for multiple days again. Plus, the majority of their advice will be to uninstall and reinstall video drivers, and I remember doing that at least 5 times back in February, with no success. I have no recollection of exactly how the problem was fixed almost half a year ago. I'm at a loss because, as previously stated, I'm not as computer literate as I'd like to be.

Anyone up to help crack this case?

Thanks, Sean