I have an ASUS N53S that I mainly bought for its RAM capacity. (I run a lot of VMs.) But as a bonus, it came with a fancy ATI video card. So I decided to install GTA 4 and plug it into a big monitor and settle down for some casual mayhem. But after about 5 minutes, it goes into hibernation! What gives?
Since I was using an external monitor and didn't need the keyboard (using an XBox controller) I closed the lid on the laptop. Gaming is compute-intensive, so my GPU and CPU were both working hard and generating heat. Closing the lid interfered with cooling. Since I have the laptop configured to hibernate when I press the power button, the heat-triggered shutdown caused hibernation.