Assuming all the hardware is good, this problem basically has three causes:
Inadequate power supply. Try a better PSU of 500 - 550 watts. That's all a 5750 needs. And because you have a CoolerMaster PSU, finding a better one shouldn't be hard.
Thermal problems. Monitoring this will be kind of difficult. After the system crashes, it is going to cool down very quickly.
Driver problems. Update the drivers.