I have a AMD Sempron M120 on my notebook which normally varies between 800 mhz, 1.3 Ghz, 2.1 Ghz. He considers some operations "simple" and thinks he could run them at 800-1.3 but in reality that poor single core runs them quite slow so i've set it from AMD Catalyst to run always at 2.1 Ghz and things been good for a while but now, quite often he locks at 800 Mhz. Few restarts and it seems that he can work normally at whatever i set him on Catalyst and i've made 3 Windows 7 reinstalls since then.

I'm really curious why this happens. How can i prevent it to lock itself again at 800 mhz?