A couple thing might be wrong. You should check and see what your power profile is in your graphics options and your PC options. Make sure they are set to prefer max performance.
You might also have a processor setting problem in your Bios. Modern processors have an option to variable raise or lower their clockspeed depending on use. This is great for normal use, but for gamers this severely limits your performance.
You might also have a processor setting problem in your Bios. Modern processors have an option to variable raise or lower their clockspeed depending on use. This is great for normal use, but for gamers this severely limits your performance.