Are you running windows 2000? I have the same motherboard and I am having some trouble with it. It will let me use my dial up modem once, if I disconnect and try to reconnect later, DUN doesnt get past authentication.

Getting back on topic, make sure the cpu is making good contact with the heatsink. It takes a lot of force to get the heatsink clipped over the cpu, is it still on there tight? There should be an option in softmenu to turn the computer off immediately if the cpu fan drops below a certain rpm. make sure its on. Did you try setting all your bios options to default? Some of the options in the bios will increase performance but make things more unstable. Is the bios up to date? Are your via 4 in 1 drivers up to date? If you get the new via 4 in 1 drivers make sure you dont choose the agp turbo option unless you are playing a bunch of games. As far as the temp goes, I have a duron 600 running at 950, and it runs around 115 F. Are you overclocking? How good is the air movement through your case? Are you using a heatsink made for AMD cpus?
Are you running a raid array? Will your computer boot up and run if you use another hard drive?

Unfortunately I think I had something like this happen to me in the past - it was a corrupted windows file and I had to reformat and reinstall windows.

This is all terribly written and out of order, but maybe you will find it useful.

Sean