That happens when it's being overclocked too much. It becomes unstable. There are a lot of overclocking guide out there for CPU, RAM, GPU and pretty much anything that can be overclocked. If you're interested on overclocking, I suggest you at least spend sometime reading them before you get to the real stuff. My personal experience with overclocking is that it is very tedious, you're basically looking for the golden ratio between your frequency, multiplier, timing, and most importantly the temperature. However, the feeling at the end when you get it right is worth it, for me at least lol