If you force a sleep ... then nothing is happening. Try this:
1. Open task manager after starting ya game .... go to performance tab... each box is about 5 seconds as I recall .... now put the machine to sleep.... wait ab0ut 90 seconds and wake it up ... see what the graph looks like.
2. Run Furmark ..... let temp graph level out. Now put machine to sleep, wait 5 minutes and come back. Remember that when you are not moving, your PC isn't doing anything. There's no pixels to redraw so GFX card isn't going anything
3. Run a movie than put machine to sleep, come back 15 minutes later and see where movie is