Disclaimer: PCWorld is not responsible if you turn your computer into a massive paperweight after trying one of the tips you're about to read. Cleaning a computer isn't rocket science, but certain techniques do carry more risk than others.
So there it is: We've spoiled the secret. The next thousand words or so will change your life for the better--or, at least, they'll add 50 friendship points to the bond you share with your desktop PC. Like bathing a cat, taking a computer from filthy to fresh can be a difficult task at best, but it's well worth the struggle, time, and messy aftereffects. (Fewer scratches involved, thankfully.)
Not only will cleaning your PC help you get rid of the gunk and other crusty unknowns that lurk within devices such as your keyboard and mouse, but you'll also be able to rid your system of the dust, hair, and assorted debris that make it look as if you had been storing it in your attic the past three years. Aesthetics aside, you'll be doing a great service for the components that help your PC stay cool: Fans can keep spinning happily if they aren't coated with dust and grime, heat sinks can cool better if gunk isn't impeding their tightly packed fins, and CPUs will benefit from a fresh, even coat of thermal paste instead of, well, whatever that stuff is that's currently caked on your chip.
Cleaning the Keyboard and Mouse
The "fun" method involves sticking your keyboard in the dishwasher and letting nature take its course. A few caveats: Gaming keyboards and wireless keyboards carry with them a greater degree of risk than standard keyboards do. To put it another way, you should steer clear of this method if your keyboard has a tiny display attached. Cover any open USB ports with plastic and tape, and, if you're cleaning a wireless keyboard, remove the battery prior to the washing. Set the dishwasher on a normal temperature with no heated drying--just air--and make sure that the keys are facing down.
If you're still rocking a legacy mouse with a ball, remove the cover on the bottom of the mouse and give the sphere (as well as the area in which the mouse ball sits) a good wipe. And for the 99 percent of you who have moved on to optical mice, a cotton swab gently inserted into the area of the LED should be sufficient to remove any debris that has collected.
Deep-Cleaning the PC
Here we go--the biggie. As tempted as you might be to just blast compressed air all over the inside of the case, resist the urge at first. If you're going the compressed-air route, you'll want to move the system to an area that you don't mind getting a little messy (as in, not your carpeted office floor). You'll also want to blast spurts of air from the inside of the case on out. No sense spraying dust back into your system, eh?
Each heat sink tends to have its own specific way of detaching. In general, you'll probably have to twist and pull up four knobs attaching the device to the motherboard, or, depending on your CPU/heat-sink variant, you might need to unlock one or two larger retaining clips or levers. Once you've freed the heat sink, use the aforementioned rubbing alcohol to wipe away the thermal paste on the underside of the component. You can also use the liquid to clean dust off the heat sink as is--but whether you're wiping the heat sink or dunking it in a bath of rubbing alcohol, be sure that the heat sink is entirely dry before you try to use it once more.
Now you're probably asking yourself why I haven't covered cleaning other parts of a PC--such as the hard drives, the graphics card, or the motherboard itself. The same tactics you used to clean the fans and the heat sink will also work for cleaning everything else. If you're just looking to give your desktop system a once-over, then I recommend that you use a combination of a vacuum hose and a compressed-air canister: Blow the dust out of the graphics card's fan and cooler, the motherboard, or the hard drives, and position the vacuum hose near the plume of ejected material so that it troubles your PC no more.
No, I'm not crazy.
The alcohol doesn't conduct electricity, and, more important, its speedy evaporation will assist you as you work toward eliminating each and every drop of liquid from the board's nooks and crannies before you reinstall it in the desktop. This method isn't for newbies, but it will definitely make the motherboard look as if it were brand-new. I don't recommend that you try to clean hard drives in a similar fashion, however--not all PC parts can survive such a plunge.