Why does my CPU usage shoot up to 100% when i start running a game.?

I have a i5 2500k processor for my gaming desktop and for some reason when ever i start certain games it shoots up to 100% and the game begins to experience freezing. I don't know what i can do to first this problem the computer is less than a year old. So how do i lower my CPU usage it has never done this... show more I have a i5 2500k processor for my gaming desktop and for some reason when ever i start certain games it shoots up to 100% and the game begins to experience freezing. I don't know what i can do to first this problem the computer is less than a year old.

So how do i lower my CPU usage it has never done this before....
Update: Radeon 6870
Update 2: 2 fans not including that fan on the cpu
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