I'm using Windows 7 RC Ultimate which was installed on a brand new 1GB hard drive. As I've been installing various programmes and utilities I've kept my Anti virus and Firewall (Bullguard) updated. I keep running a full scan but cannot solve my problem. I also run various malware, spyware, call it what you like ware, without result. My computer freezes for between ten seconds and four minutes, and a white "mist" or perhaps a translucent white veil covers the screen. Nothing works. CTL, ALT, & DLTE will sometimes bring up the option for Task Manager, other times it won't. I've got 4GB of RAM which Windows tells me is working OK. Sometimes the computer won't freeze but the sound seems like someone is being strangled - it becomes very garbled and I have to cancel the sound. I've tried re-booting at this stage, i.e. before the computer totally freezes and the white mist appears, and this sometimes fixes the sound and it lets me have email and perhaps one other programme running without slowing me down by 90%.
I've got a Gigabyte motherboard GA-965P-DS4 which I'm told is a good board. The processor is an Intel Core 2 CPU 660@2.40GHz, 2,400 Mhz, 2 cores.
Does anyone have any idea of what uis going on here, please.

Try changing the UAC (User Access Control) settings.
Also try different graphic card drivers.
Note, only a few Antivirus/antimalware programs work on Windows 7 so be careful what you install.