Random Crashes

Hey

For the last 5 days or so my computer has been crashing randomly. At first it seemed to be happening when i was in games, the Frame rates would start to drop until it freezes once this happened everything freezes but sometimes(not all the time) the mouse will still move but nothing is clickable. Other times ill be on ventrillo or skype or listening to music and all of a sudden the music will just 'glitch' i suppose it just gets stuck on the same piece of music and nothing i can do stops the noise then the system slowly starts to slow down until it crashes. This kept happening while i was in games so i thought maybe its over heating, but last night i was just browsing forums when it happened but this time the mouse also stopped but i could still communicate with people on skype so its like some parts of teh system crash and others dont.

Im really confused to what is happening, i have all the latest drivers installed etc. Could it be a faulty graphics card? (i have a 8800GT) or could it be over heating etc?

System: Dell XPS 420... sigh

Intel Q6600 Quad 2.4GHz (NOT overclocked)
Nvidia 8800GT 512MB
4GB DDR2 RAM 1000MHz
Windows vista 32bit


Please let me know if theres any more information i can give if it helps.

Hey

It kept happening again repeatidly 2 nights ago so out of stress i just formatted the hard drive and re installed windows and now after a day it hasnt crashed once so i think whatever the problem was its gone now but thanks