Computer running very slowly at times

I have a Dell Inspiron 600m notebook computer. There are times, particularly during games or when the screensaver comes on, that the computer seems to process in slow motion. I will click a button, and it will take a few seconds to register that I clicked it, and then it will take even longer to process it. In games, the computer seems to be working in slow motion and choppy. When the screensaver comes on, it takes several seconds to return to the main screen after moving the mouse. If I restart the computer everything seems to be fine for a little while, then it starts again. I have done a complete system restore on my computer but it did not help. I still have 3 years of warranty from Dell, but they claim it is a software issue, which they now say they won't cover, and they won't help me figure out what the problem is. Does anybody know of anything that could cause this to happen? I will never buy a Dell again.

 

Have you run a spyware/adware scan?
Have ypou got much fee space on the hard drive?

 

I just completely restored my computer so I have no adware/spyware, and I have over 40GB of free memory. I also have 1.25GB of RAM.