Thermal Shutdown

first, try to check the heatsink of the processor if it is full of dust and the air flow from the processor fun cannot penetrate to the processor.
second, double check the brackets that holds the heatsink to the motherboard, bcoz in most cases for socket 478, those bracket will easily get cracked due to aging, the reason the heatsink will not totally hit the processor.
third, remove the thermal pad on the heatsink and replace new one.
if you're done with the above mentioned, and still the same problem exist, may be there is something wrong with the sensor of the motherboard the reason it registered a wrond temp of the processor, but this cases rarely happens, but still it does.