Could be your power supply - the more laod you put on the gfx card and the hotter it gets, the more power it drains, so if you power supply could fail to deliver the required power and that causes the gfx card to fail, so the gfx driver stops working and you get the error "device hung".
Try open your computer case and see if that helps, typically power supplys go down in efficency if they get hotter as well.
