If all your drivers are OK, it is most probably about memory timings. I had the same problem. In my case everything worked fine but the cloth simulation. It just locked up. I adjusted my memory timings and everything works fine now... Nforce3 and 4 boards have a lot of memory parameters. If you are using your old RAM, you might need to work on them...I had to switch my sticks and adjust the timings to get a stable system at 2.25 Ghz with my Winchester 3000+ (Yes it it overclocked from default 1.8 Ghz)