that temperture for the
CPU is getting on to high even for an athlon.
Have you cleaned and checked that your heatsink/fan combo for the
CPU is working OK. You might find that all you need to do is give that a good clean and reapply some fresh thermal compound and it could solve it. Easiest way is if you have an air compressor handy get a blowing tool and stick it in there and blow the dust out, if you dont have a compressor just lying around then you can buy a can of compressed air from lots of hardware stores. If none of the above is true then take the
HSF out and do it.
It does sound like a thermal shutdown.
Good luck.