Your cpu speed and voltage change as the cpu needs them to. You don't want to be running at full speed and voltage 24/7 when the cpu is idle, it's for efficiency. If you go into your power settings in Windows you'll probably see you're on balanced mode, if you put it on performance it'll run your cpu at 100% at all times, but it's just going to shorten the lifespan of the cpu and draw more power.