Come on people, answer the question...
My advice is to buy an HD7850/70 2GB video card. Here's a recommended model (though please give a BUDGET next time):
A GTX660, or Ti is another option though you'd have to verify benchmarks vs prices.
*Please be WARNED, there appear to be quite a difference in quality. There are cheaper cards than I recommend but I caution you to be careful. If in doubt, get one of these.
1. remove current NVIDIA drivers
2. Turn PC OFF.
3. Swap cards.
4. Turn PC ON.
5. Download and install the latest drivers.