Could you download SpeedFan and check the numbers every couple of minutes?
My laptop is in a weird state right now. The hinges have started to pull the top and bottom shells off of the laptop, which has allowed heavy amounts of dust in, which causes significantly more heat. Meanwhile, the pin for the power plug (which is required since the battery is completely dead right now) is a little bit wobbly, which is caused by a micro-fracture. Whenever the laptop overheats, the micro-fracture becomes much larger, and the power plug no longer functions, and the laptop shuts down.
You might have a broken pin. What is the state of your battery, and do you use your power plug/charger?