As I understand it, it gets to hot. The air don't circulate as it should and the fan keep running at full speed to attempt to cool things.
The most common cause is dust accumulation.
Over time, dust will accumulate on the heat sinks and also block the air channels.
It also looks like you are past the point where only using compressed air in the air intake and outtake could help.
You need to open the case and remove as much dust as possible.
Once it's done, close the case and you're done.
You should dust off your computer about once a year, more often it you are in a dusty environment.
Another cause specific to laptops, is resting on a bed, cushion, blankets or any other soft, cushiony, surfaces that can prevent adequate air circulation.
In tht case, place it on a flat, solid, surface, like a desk or tabble.
Electro, May 2011
