I'm sure this is one of those beaten horse questions but i've just replaced my Athlon 64x2 with a AMD Phenom II x4 3.0 ghz processor. The board i'm using is an Asus M4a78 Plus and does support the processor. Running Win 7 x64 with the athlon i had ZERO problems. I just wanted a little more speed so I got the x4 Phenom. This is when the problem started.
I knew immediatlely to upgrade the bios - this is what i did first. Popped in the processor and it fired right up - right into windows. So i start applying patches (both Asus and Windows) and this is when i noticed the problem. After about 5 minutes of doing ANYTHING - the system crawls to a halt - doesn't lock up completely - the apps respond but VERY slowly (it took 7 hours to install new Catalyst drivers). If i just let it sit for 5 minutes - no response from any application and nothing is showing in task manager as not responding. The graphics board is an older 7950GT but i'm not a heavy gamer so i'm not too concerned about that.
I've been crawling the net for the past 2 days trying to figure this out and can't find anything other than possibly the board is just not capable of running the processor. It's not on the recommended list for AMD but it clearly states in every spec i've read that it will support it. All tests are showing full 3.0 speeds x4. I know my memory needs a bump (DDR2-6400) and it's possibly the bottleneck - but i can put the athlon processor back in and ZERO problems - runs fine.
I would suggest trying a Windows reinstallation. Might not be seeing the CPU properly.
Thats supposed to be a link to your mobos CPU support list but man ASUS website is being slow and crappy today. I checked your mobo model and it can support up to a Phenom II X4 965 C3 stepping, so its not that your mobo can't run the CPU its probably that Windows doesn't like you swapping out the CPU.
I just pretty much confirmed that it is Win 7 not liking the CPU swap - I put the old processor back in (with all the same updates) and now i'm getting the same problem with the old CPU. OH well, Time to grab a 6 pack and reinstall.
Thanks for the confirmations. Needed a 2nd opinion.