I need help with graphics/CPU problem

[Beribimba]

I'm having a problem running games. My system is as follows: Windows XP, 512 MB RAM, 27 GB hard drive, 2.4 Ghz Pentium 4,
Radeon 7500, DirectX 9. All these games that used to run perfectly smoothly on my system now give me choppy graphics for a few seconds, then smooth for a few seconds, then choppy again. They are not necessarily graphics heavy games, either. Even very simple things are having the same problem. I've tried everything and can't fix it! I think that it might be a CPU problem, however, and not necessarily a graphics problem. My laptop whines (either the motor or the fan?) when it happens, but it didn't in the past. I've checked my processes and cancelled everything unnecessary. I've cleaned up my registry. I've deleted temp files. I've defragged my hard drive. Nothing helps. If anyone else has any suggestions, please help! Thanks.

[rakesh_1024]

Removing the graphics card and cleaning it(especially the part that goes into the slot) might help