I would not rely entery on the temp settings from your bios. There are very few things that shut a pc cpmpleatly down,
You have checked your chip for overheating.
Run a disk check, select the option that says look for bad sectors, ( it will ask you to shut down to run it )
Run a memopry test.
If your chips not overheating, will propbebly be your disk.
somtimes in the bios, it stors the last fault condition, ? make sure xp is updated as i think there is a upgrade for the chip driver if its a duel core chip