You probably just pushed the OC a little too far. You don't have to go back to defaults, but you might have to tweak your settings a little (a little more voltage, or a little less clock speed) to get it stable. You can keep a solid overclock, especially sine you are only hitting 52C, which is by no means too hot. One thing to check though, is to see what your BIOS setting for the overheat shutdown temp is- it could be set very low (set to shut down at 52C) if thats the case, you can up that auto-shutdown temperature up to something in the 65-70 C range and be good to go.