Close your computer. After you've finished dusting, replace the side of your machine and any screws. Once the machine is tightly shut, return it to its usual spot and reattach the power cord and other cables. (You might consider cleaning this entire area to remove excess materials that can contribute to dust intake.) If you flipped the master power switch on the back of your machine off, be sure to turn it on again or your machine will not start. A clean computer will run significantly cooler and last much longer than a computer clogged up with dust and debris.