I DID try the insulating material idea, using some mica from an old capacitor. It worked for a couple months, and then the laptop shut down again, but only with certain graphics-intensive programs.
The reason your laptop is shutting down might be related to something called "throttling up." This phenomenon occurs when the CPU receives code that warns it that some processing-intensive activity is about to occur, and the CPU throttles up to max. Mobile CPUs live by that philosophy. The increase may be interpreted by Windows as a threat because sensors indicate the increase in heat caused by the CPU activity is increasing faster than the CPU cooler can remove it, so it shuts the system off. Certain Toshiba laptops had this problem from the factory, so as a solution, Toshiba released a new BIOS that reduced CPU throttling, causing multimedia performance to be herky-jerky in a machine that was billed as a multimedia system. Toshiba owners went nuts!
But you don't have to resort to that. There are programs now that allow you to control throttling from Windows, and they're worth a try! Check this website for more info:http://www.oldskool.org/pc/throttle
Good luck, and remember what Tim Allen said in the movie Galaxy Quest: "Never give up, never surrender!"