My friend has the same problem, he was running Quad core 2.4GHz and 6GB RAM. It could be anything to do with the drivers or the registry files, or your actual RAM. Here's what you should do
1. Clear your RAM cache. Get as much free RAM as you can.
(Another option here is eBoostr. You could download eBoostr with a memory stick, and use your memory stick as RAM if that helps. (or readyboost it.))
2. Disk Cleanup. Clean up your disk, get rid of all the useless crap that might be messing with your computer.
3. Registry cleanup. Check your registry files for corruption, it might be to fault.
4. Virus check. Make sure you don't have any virus play hell with your graphics settings.
5. Defragment your computer. This will reduce the risk of corrupt graphics drivers, or any drivers for that matter.
6. Update your PC? Maybe you have updates released by Windows (I take it your smart and using a PC) designed to get rid of this glitch. Worth a shot.
Hope this helps.