To uninstall your current video card drivers > go into Device Manager > Expand Display Adapters > Right click your graphics card > Click Properties
Select Driver tab > Click Uninstall
Have you checked the temp on the graphics card? If not download Speedfan from the link below to check it's not overheating.
Download SpeedFan - Access temperature sensor in your computer
Also you can try running the game on just one core, I've used this as a workaround to get older games to play properly on 64bit. To do this start your game > ALT+TAB out > Press CTRL+ALT+DEL to get into Task Manager. Under processes select the games .exe > right click - select Set Affinity > Remove the tick from
CPU 1 > Click OK. See if that helps. That only works as a once off - the next time you start the game it will use both cores again.