Computer keyboards have a fairly long lifespan, but they do develop problems over time. Everyday wear and tear coupled with design flaws and accidental damage can take a large toll on your keyboard. The keys in the home areas are particularly susceptible to wear, especially if you use your computer for gaming. Among the keys in the home area are A and Z, while the number keys see use in many games by default.
Clean your keyboard. Use the butter knife or screwdriver to gently pry up each key, then use the can of air to blow away any loose debris. Follow up with cotton swabs dipped in the cleaning solution and wrung nearly dry to remove more stubborn debris.
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Check the hinges and nubs under the problem keys while the keys are detached. Hinge and nub damage is a common cause of non-functioning keys. Replace damaged pieces, then reinstall the keys. Test your keyboard to see if this solved the problem. Not all keyboards use hinges; they're more common in laptops.
Try a backup keyboard to see if the problem really lies with the board. If the board itself is the problem, you should replace it with a manufacturer-approved part.
Update your computer's drivers. Corrupted, out of date or missing drivers can sometimes account for problems like this. If your keyboard came with driver software, try using it instead of the ones installed on your computer by default.
Refresh the contact coating on the key nodes of your keyboard's circuit board. A graphite-based spray works best and should be applied using a small tool such as a screwdriver. Do not apply the spray directly, as it will short your board completely, rendering it unusable.
Things You'll Need
Flat-head screwdriver or edgeless butter knife
Electronics cleaning solution (rubbing alcohol and water mix)
Replacement keys, nubs and hinges
Graphite contact spray (Graphit 33 from CRC Industries-Kontakt Chemie is recommended)
Make sure when you buy the compressed air that it is designed for use on home electronics. Some brands can leave a sticky residue that will make things worse than they were before cleaning. Keys, nubs and hinges are usually sold together.
Avoid using a large amount of cleaning solution. Runoff and drippage can damage your computer. Be careful when removing the keys from your board. There are small, easily damaged pieces of plastic holding them on in most cases.