Please help Vista64 is driving me mad!

Hi

I am really going mental about Vista 64 and i really need some help. I built my system about a year ago and had no issues until about 3 months ago, the computer randomly freezes and lets out a squealing noise from the speakers not the box. I thought it could be the sound of death with creative sound cards but i bought an asus one (Xonar) and that just made a different noise (also it is the worst sound card ever). When the computer freezes the bios clock is still going but i cannot exit the program and need to restart. This mainly happens in games completly randomly (5 minutes or or 4 hours in) but has also happened when on the desktop.

I have updated my bios, changed the sound card and even went back to onboard sound. I also reinstalled vista and avoided the updates and all my drivers have the latest updates.

Can someone please help as this is making me go mad!!!!:cry

my specs are as below:
Motherboard: Asus Rampage extreme intel x48
BFG Geforce GTX 260 OCX
Intel core 2 Quad Q9450 2.66
Corsair 8gb DDR3 DHX 1600c7dhx 2x4GB
OCZ Elitexstream 1000w sli ready powersupply
Vista 64bit Home premium
750gb Sata harddrive x2
Creative sound blaster X-Fi Xtreme gamer 7.1 sound card