Dust bunnies build up inside computers over time and cause this kind of thing by putting a blanket over components so the heat can't readily escape. Every 6 to 12 months you need to get a can of compressed gas and blow it through the air intake ducts on the bottom of the laptop.
My son's computer is running Vista, on the dell studio 1535. It had been giving him a few problems with the blue screen of death, but I put it down to the weather and games etc. Yesterday morning, he attempted to boot it after it had been off for 11 hrs, It began to start up but then instantly over heated and shut down. I am at a loss...any ideas?