Have you tried Googling the problem? They say dogs are mans best friend, but I think it's Google
Otherwise, it could be any number of things. Maybe your PC is getting too hot. Often times PC's will automatically throttle the power of the system when it gets too hot in order to compensate; this is especially painful on notebooks! Make sure you have plenty of air flow to your PC.
Also, maybe its not a video driver issue. Try setting your Windows quality to "best performance" and also try increasing the size of your page file.
Right click on My Computer -> Properties -> Advanced - Performance
Or something like that, I've been using Vista far too long
Anywho, find your way to the "Visual Effects" tab under your performance options. Set it to "Adjust for Best Performance". This will make Windows look like 98, essentially, but it will run better.
Next go to the "Advanced" tab in the same window. In the "Virtual Memory" area click the "Change" button. The "Virtual Memory" box will pop up and you can change the size of the paging file here. Make sure "Automatically manage page file" is unchecked. Now set the maximum and minimum size to the same thing, I have mine at 4096. Click "OK" and you're done. You'll have to restart.
Only other thing I can think of is go into the task manager and make sure you don't have to many services and processes running. I hope this helps. Beyond these suggestions I wouldn't know what else to tell yah.