Laptop Shutdown

I have Micron PC Transport GX3. It performs fine when using normal applications and DVD viewing. When I try to play games, it plays for a few minutes then shutsdown without warning. The pc does not have a problem booting back up. It is running a Radeon 7500 ATI. I have noticed that the laptop does get extremely hot. I have downloaded graphic accelerators, but to no avail. What type upgrades can I do to be able to play video games? And also what can I do to make the laptop run cooler?