I struggled with this one for a while on two separate systems with different motherboards, different video cards, and different memory manufacturers and speeds. So after trial and error, thinking that it was the video drivers and windows update (still possible due to system changes in update) it turns out that the program Core Temp was conflicting with windows 7 upon start up.
The program itself is fine, but it cannot start with windows because I suspect, that it loads before the AMD chipset drivers load. I know this because, it was a fresh install of Windows 7 Home 64 bit, and I downloaded Core Temp before I installed the chipset drivers. When I started Core Temp, the system froze. Later it would work but only after the system was already operating. Enable it to start with windows, and the system freezes just after login, and the screen goes black with no video output.
This only happens on my AMD systems. My Intel systems are not affected. Also, both AMD's are FX series (4100 and 6100) and both use AMD video (HD5450 and HD5770)
Boards are M5A78L-M LX Plus and MSI 760GM-P23 FX.
I hope this helps someone since it took me a few days to figure this out. I know a lot of overclockers out there use Core Temp to monitor CPU's under Prime 95 operation, so I figured I'd save you some time.
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"the program Core Temp was conflicting with windows 7 upon start up" - that might mean something to someone and might be a fix for you but I'd still be a bit wary, it could actually be something entirely different. The program is 32 bit application and it could possibly conflict with x64 oses.
Correct, which is why it is a possible fix. It could be also that Core Temp is attempting to use functions that other, similar temperature and speed monitoring programs are trying to use. I guess I should have been more specific that it's a theory about the chipset drivers. But it makes sense, and so I would recommend disabling any thermal/speed monitoring programs and see if it hangs up. For all I know it could be a symptom of a larger problem with the drivers. I have yet to try any other programs with similar functions.
Just thought I could save someone like myself a little time and effort. I looked at 50 threads with no luck over the past 4 days.