Before chunking it in the garbage, get a can of compressed & see if you can't dislodge a big clump of hair/dirt/etc.
Overheating is almost always from clogged air flow areas. If the fan can't expel the hot air, the heatsink & processor keep heating up. At a certain point, the processor can't perform it's job & the system shuts down, by default, to keep you from having a fireball on your lap & to reduce damage. Prolonged operation will fry your motherboard eventually, but I have "fixed" several laptops just by cleaning them ( If you are adventurous, you could try removing the keyboard & top motherboard cover. This will allow you lots of space to clean).
Jay W C
July 2008