You said your CPU is running on 99% on all cores, can you show us your CPU temperature? Odds are that your CPU fan has not been mounted properly. However, if you are playing other games intensively, and working just fine, then my guess is that you probably got some malware or virus in your system that is turned on when running programmes. Do a system clean up, defrag, restart and see if the problem happens again.

But do check your CPU temperature!