Random system hanging

[Rustymandela]

My current PC keeps randomly crashing, or hanging. I have no idea why as it seems to happen at random- I suspect it is a CPU issue though. I have ruled out the power supply, ran memtest for 24hrs with no issues, reinstalled Vista but without additional components I'm not sure what else to try. I also removed a soundcard, which seemed to reduce the incidence but it still happens every time I use the PC, whether it be immediately after i log on, or at random 3hrs after whilst reading a webpage.

Any ideas? I can't really swap out components to test them as I have no replacements.

 

[Rustymandela]

Should have said:

Q6600 G0 @ stock
Asus P5N-E Sli
(brand new) Corsair 650W TX
4x 1GB OCZ DDR2 800MHz/PC2-6400 Platinum XTC