Today i finished building a new system, for a friend of mine, and everything was going smoothly. Got it all put together, installed Windows 7 Ultimate, booted up, uninstalled many programs that I didn't want, installed Mozilla Firefox, and was in the middle of doing two things when it first froze. I was 1. checking for windows updates, and i was 2. downloading the Nvidia 301.42 graphics update. The "freeze" was interesting though because a few things on the screen still functioned such as the sliding green bar on "checking for windows updates". I restarted the system, and once it rebooted I began downloading the Nvidia graphics drivers again. Within 30 seconds it had frozen. Restarted again and tried to check for windows updates, froze within 2 minutes, again though the green swiping bar was still functional. I then restarted and attempted to run an "Sfc/scannow" in command prompt, but the computer then froze (again, a minimal function such as the blinking dash in command prompt WAS still blinking).
I have just completed an sfc/scannow by running the computer in safe mode. No problems were found.
Update(2:47PM): I allowed the computer to sit for about 10 minutes, and it didn't freeze. I then clicked on the start menu bubble and the computer froze. Once again, i can still see a small activity. This time, the vertical line in the start menu search box is blinking.
System build :
ASRock 970DE3 motherboard
AMD FX4100 am3+ 3.6ghz quad core
Nvidia GTX 460SE (not new, but was taken right out of a perfectly running computer)
8GB of PNY DDR3 1333 Ram
WDC 1TB HDD
630w Rosewill PSU
Sounds like a memory access problem I've had one and the PC acts strange to say the least. I see you have 8gb of memory is that 2x4GB, If so try with just one stick, if the same result try with the other, if the same result try the other slot with each stick. If no freeze in any of the configurations you got a bad stick of RAM which isn't all that uncommon. Good Luck
If this is not the issue it could be an overclock issue like an under voltage if you are running one or your RAM speed may be wrong in BIOS.