Sounds more like overheating to me.
Try enabling vsync, fixing the framerates should take some stress from the pc.
In the long run, it might be better to find out if it is overheating and which component might be affected (GPU or CPU).
You could run some stress tests while logging your temperatures (e.g. Prime95 for CPU or Furmark for the GPU) to see if that causes a crash, as well.
