Sounds like the Processor is overheating and getting hotter than 70C.
The Maximum Operating Temperature for the FX 8350 is 61C. After that it starts to throttle and if it continues to overheat shut down the computer.
Possible causes:
1-Thermal Paste is bad and not as efficient in transferring heat.
2- CPU Cooler is defective and not cooling as before
3-CPU Cooler is not strong enough to remove heat from a 125 watt TDP Processor under very heavy loads.
4-CPU Fan is not working properly or is defective or obstructed
5-Poor air circulation in the computer case
Stress test the CPU and see how high the temperatures is showing or if it shuts down during the Stress test.