Computer experts I need your help! (more details inside)

I have an HP Pavillion g6 notebook and it has problems. It began a few months ago. When I try to run a game, the screen has mixed colors and after that a blue screen appears. Then it shuts down and keeps restarting all the time. Also sometimes when I move my notebook, when I place it down it stops working and reboots. I sent it for service but they told me that the problem was that it had dust. Some days later it happened again, so that was not the problem. What could be the problem? Has that happened to you?