Is this an issue with only one game, all games, your desktop? What kind of monitor do you have, CRT, or LCD, did you move it someplace else when this occured? Did you just install this card? If so, it may be that you didn't get it seated properly, make sure the clip on the AGP? slot clicked properly. Remove it and reinsert it and try it again. Also, what size power supply do you have, it might be power related. You didn't say you have a GT version, but if you do, have you got the extra power line plugged in to the card, if you have a GT, it won't work right without this.
As far as the drivers go, I really don't think this is a driver issue, but I could be wrong. I'm not trying to put down DNA drivers, but I have had issues with them several times. I don't use them anymore, but there are a lot of people that are very satisfied with them. In a case like yours, my opinion is that you would be better of using the official nVidia drivers, at least until you get this sorted out, after all, they are the real drivers that were made to work with your card. If you want to try a a seemingly endless supply of beta drivers, go to
here, and click on downloads, Forceware drivers. I find the 67.03 drivers work well for me on my BFG 6800 GT OC, if you want to try the beta's these would be a good choice, even though there are a lot newer ones. You will see so many different drivers it will amaze you. Also you can look for modified drivers of which there is also an abundant supply.
You should be able to change drivers without any danger, following BringingHeat's instructions above, but I would download the new drivers first so you will have them ready. As he said, be sure and use Driver Cleaner after you do the uninstall, to clean out any last remnants of the old drivers.
If you cannot resolve this issue, I would call tech support for the card, and talk to them. Could have a deffective card.