Oh the old story. Just because a set of components worked perfectly well in a previous life (or box) doesn't mean to say that they're going to cohabitate successfully in a new one. In this case, no doubt others will advise differently but I'll revert to my normal extreme. Firstly make sure that everything is properly connected and none of the cards wobble. Try to work backwards, unistalling the software that you think caused the problem (I suspect you've done this already). Make sure that you only have one of the Nvidia drivers on board - the older cards could get funny if you didn't uninstall the old drivers completely before installing the new - there's a program around called Detonator Destroyer which was effective in blowing old ones out of the water. And if all else fails, a clean install of the OS and known good drivers may be in order (well, it might be the quickest way to fix matters). Then go gently.