Other than power spikes, spilled beverages and falling down the stairs, few things shorten a computer's lifespan as much as accumulated dust. After just a few months of normal use, a fine layer of dust will accumulate on a computer's circuits and ventilation ducts. If you have pets, animal hair and dander is an even greater threat. Much like wearing a wool sweater when you're jogging, this makes it harder for the computer to dispel heat. If neglected, the build-up can plug fans and the ventilation system, making the computer severely overheat. Cleaning inside a computer takes just a few minutes. All you need is a can of compressed air.
Disconnect the power cord and every cable attached to your computer. Open the case. How you do this depends on the model. With the HP desktop shown here, just loosen the large screw and slide the side panel off.
Remove the battery if you are working on a laptop, then remove the bottom case panel so you can get to the fan. For most laptops, including the Dell laptop shown here, you'll need a small Phillips screwdriver to remove the screws. Once the case is open you can see the CPU fan.
Take the computer outside, unless you don't mind a lot of dust in your house. Most of the dust forms a micro-thin coating that can be hard to see. Once you start cleaning, however, the dust will fly everywhere.
Spray the inside of the case with a can of compressed air. Keep the can upright at all times and never shake it to prevent the liquid refrigerant from leaking onto your electronics. Use short bursts of two or three seconds. When the can gets too cold to hold, set it down for a few minutes until it warms up again.
Blow compressed air on the external fans from the inside and the outside, always using short bursts.
Blow air on the CPU fan. If the fan starts spinning, hold it in place with your finger so it doesn't get damaged.
Blow air around all of the wires, over all the circuit boards and memory modules. Inspect the computer to make sure all of the dust is out. Because the dust blows everywhere, you may have to repeat the process a couple of times.
Wipe the fans and ventilation grills with a cotton swab dipped in rubbing alcohol if they're particularly dirty. This shouldn't be necessary in most cases, unless you work in an especially dirty environment. The laptop shown here was exposed to quite a bit of campfire smoke over the summer.
Clean your computer at least once a year. If you have pets, or if you keep your computer on the floor, clean it every six months. Pet hair can accumulate quickly, as seen in the Mac Mini displayed here.