I had a VIA motherboard, as did my brother. We both replaced them because of problems we were having with our GeForce cards.
If you do have a VIA chipset, try this link for some help as well.
http://www.viaarena.com
We found help for some of the problems we had there. It might help you as well.
My last AMD cpu was a 5x86, so I don't know much about the lastest chips they have. I do believe that the AMD Irongates (not sure what that is) had some kind of problem with GeForce cards. If this is your case, check out the nVidia site for information on that.