Over time, dust and lint can accumulate in a laptop's heatsink and fan, restricting airflow and causing the fan to run at higher rpms and to cycle on and off more frequently. In severe cases, the airflow can be restricted enough to cause the laptop to run warmer than normal, causing the power management software to throttle back the CPU & GPU, reducing temperature and performance.
In extreme cases (and typically after many years of use), a system that has accumulated large amounts of dust and lint can become quirky, exhibiting hangs, crashes, or even unexpected shut downs.
You can keep your system running cool by cleaning the fan and heatsink with compressed air from a can. These can be purchased at most office supply,home improvement, hardware, or electronics stores. With the system turned off, simply blow air through the vents on the left side of the system. This is typically enough and may be good preventative maintenance to do once or twice a year.
As a system ages, or if used in a particularly dusty environment, a more thorough cleaning may be required.
1) Power off the system, remove the battery and AC connections, and turn the latop over.
2) Using a philips screw driver, carefully loosen / remove all the screws on the main access compartment on the bottom of the system. Once the screws are loosened / removed, find the finger relief along the edge of the panel near the center of the system and gently pry up the cover. Be sure it opens easily, and that no screws remain. Behind this panel is the HDD, Memory , Wifi card, and cooling fan.
3) With the cover removed, locate the fan at the corner of the chasis. It is held in place by 3 screws at locations marked 1, 2, and 3 in the photo. Carefully remove these screws. (A magnetic screw driver helps) Gently unplug the fan power connector marked at location 4 in the photo.
4) Carefully lift out the fan and use the can of air to blow dust out of the fan, cleaning off the fan blades and the housing.
5) Next, direct the air through the outside vents so that the dust is blown out of the heatsink radiator fins in the direction of the arrows. As the fan blows air in the opposite direction normally, this reversed airflow should remove dust that has accumulated on the fan side of the fins. Blow away any dust that settled on the system.
6) Carefully re-install the fan by reversing steps above. These are the same steps to follow if you were going to replace the fan (if it failed to run at all).