1) Check the device manager for yellow flags.
2) Update all your drivers.
3) Try trimming the visual effects. Go to Control panel->System->Advanced system settings, click on Advanced tab, then under Performance, click on Settings. Now click on Custom and uncheck some of the animation related boxes.
4) You can also try run the Troubleshooter (click start, then search on Troubleshoot).
Test your memory using memtest86 CD for 5-6 passes.
Check the Event Viewer to google repeat errors text to find how others have resolved them.