Fans: Check the power supply fan for airflow and the processor fan for movement at least every six months. Take the case off of the computer and turn the computer on to check the processor fan. If one of the fans stops while the machine is on, you'll need to replace it immediately to prevent further damage.

Computer Case: While the computer case is off, use a can of compressed air (available at most office supply stores) to blow out the dust. If you want to save some money on compressed gas, remove the cover(s) from the computer and go to your nearest gas station. Blow the dust out of the computer case with a blow gun or tire inflator. We use an automotive-type compressor and blowguns to clean equipment at our shop. (Only blow dust out of the computer case, not your PC's innards.)

One caveat: If you are using canned or compressed air, use short bursts to avoid condensation.

Drives: Clean the floppy drive(s), CD drives, and tape drive to help prevent errors during use. 

          Clean with either Simple Green or 409 spray. Be careful not to get the insides of the drives wet.

Tape drive: If you have a tape drive, you may be able to clean it by using a long Q-Tip dampened with rubbing alcohol. Open the door and clean the rubber pinch roller and head located inside. If you have a DAT, SLT, or DLT drive this may not be possible since the pinch roller and heads are too difficult to access.