Computer Housekeeping

Caution

Before you work inside your computer, eliminate the hazards. The first hazard -- electrical shock -- is to your personal safety. Disconnect the power cord from the back of your computer before you open it.

The second hazard is Electrostatic Discharge (ESD). For example, the electrical energy you pick up walking on a carpet is enough to blow out almost any electronic part you touch inside your computer. Just moving around in your chair can generate enough to damage sensitive parts. To prevent damage from ESD, always touch the bare frame before you put your hand or any tool inside your computer's case. Better yet, keep one hand or your arm touching the frame, while you are working inside your computer.

Keep it clean

You'd be amazed how much dust and crud can accumulate inside your computer in a couple of years. Very few have intake air filters (most people wouldn't know to clean them, and the result would be even worse) so the dirt just collects inside. What happens if you don't keep it clean? To paraphrase Professor Tognazini (Heald College -- San Francisco, circa 1957), "You shorten de life of de computer!"
http://blogs.pcworld.com/tipsandtweaks/archives/003406.html -- Steve Bass's tips
http://www.google.com/search?q=clean+inside+computer -- more at Google

CMOS battery

The CMOS battery maintains some of the basic settings for your computer, as well as the system clock. If the clock loses it's setting when you turn off your computer, it's time to replace the CMOS battery. It's usually a thick disk about the size of a quarter. They usually last from 3 to 5 years.

CMOS Battery Replacement:
http://www.liverepair.com/encyclopedia/articles/cmosreplace.asp
http://pcsupport.about.com/cs/cmos/index.htm
http://www.google.com/search?q=replace+cmos+battery