It may be because LW uses Java, which Java is not RAM efficent and uses VM.

This can cause heat conduction, by using the RAM and Hard Drive more than the system is used to. This might be caused several different ways. Manufacturing defects that don't manifest themselves, until the machine is put under a load. An Improper or Inadequate cooling system. Under powered power supply --- the system needs more power than the power supply can provide. The last item sounds like it may be the probable cause --- Most power supplies have a thermal safety switch, which, when it over heats it will stop supplying power, until it resets, causing the system to reboot. There may be other similar safety features within your system that have the same function.

Hope this helped explain things about overheating a little better.