Is it overclocked? If so it may be running on the edge of it's maxiumum alllowable speed. It could also be overheating, overclocking creates much more heat and the processor can run much hotter if your cpu cooling system isn't addequate. If it's not overclocked, and is an older unit, could be the cpu fan needs oil or repalcing, or heat sink fins have collected enuff dust over time to decrease it's efficiency. I f none of the above sound right, we may need more info for diagnosis. You could try reseating the memory? Power supply getting weak? Could be one of many things. Suppose it could be software, but usually one of the above. 
edit- I now see by your system stats you are overclocked by 200mhz. Try increased cooling or slow it down one notch, I think this will cure your problem.