Well, when it comes to your PC there could be a whole number of issues. There could be a few possible fixes, but I do apologize as it is really tough to figure something like this out without the physical computer in front of me. You could open the bad boy up and put a can of air to it - clean out all of the dust that could be piling up on it. Also, you could always try updating graphic drivers on there. Also, does the laptop happen to overheat?
One good way to diagnose would be to bring it over to a Best Buy to see if their Geek Squad could do anything with it, but alas that does cost a bit of money to do so.