Irregular Freezes help needed

Hi I am desperately needing help.


My system is:
A8n SLI
2 gb DDR 400
XFX Geforce 7800gtx
amd 4000 plus
the power supply is Enermax I dont recall the model, I will search for it if necessary.

From time to time and for no reason my computer freezes, the image stays static and the music in case I was listening to one just stops, there is no response from the mouse or keyboard, the keyboard itself stops working since the caps lock does not switch from on to off, and only reboot brings it back to normal.. for a while. It can happen when I am playing watching movies or listening to music or when I am doing nothing at all (it also happens in safe mode).
I have tried everything I can remember, format, memtest, insane virus scanning, asus probe does not find any problem with temperature or voltage so I take it has nothing to do with the power supply.
Even if anyone has no idea on how to help me I would like at least to know if any of you has ever known of anyone with this kind of problem, thank you.

Ok thanks for the info I will try one of those steps at a time to check if any of them changes anything, could you tell me what does IDE SW, cool n quiet and CNQ do to harm my pc in this way ? thank you.

What OS are you using?