Alright so I have been having this problem while playing Games on steam. My CPU and GPU both overheat to over 55 degrees Celsius. I do have the stock fan on my processor. I don't think its my power supply either.
CPU: AMD 8150 ( Not Overclocked)
GPU: ASUS HD7750 1GBDDR5
MB: ASUS M5A97
RAM: 8 GB Ballistic
PS: 700w OCZ
Case(if matters): Thermal Take V3 Black AMD
55c is about the limit for error free use of an AMD chip... though some can stretch it up to 62c. your problem is the stock cpu cooler. replace that and your temps will come down, and you'll no longer lock up.