Keyboards with individual switches. Press repeatedly on the push rod until it works OK and also displays its character on the screen. At first, the cleaner may cause the key to fail to display its character. Some keys stick due to stickiness on the keycap bottom surface.. If the key sticks in the fully down position this could be the problem. So you might need to clean this this area too.

If you decide to push it sideways, use a small screwdriver to push sideways with while pushing the key up and down with both your finger and the screwdriver. You should push it sideways in one of the four directions and try different directions. What you are doing by this is attempting to force out a foreign particles that are rubbing on the side of the key's push-rod and making it stick. Again, the problem may return later.

Always test the key just after fixing it and a short time later. To test the key, push it down very slowly and see if it sticks. Also push it sideways a little as you're pushing it down. If you hit it fast or push it straight down, then you may not observe the stickiness. This test will detect a key that seemingly works OK but is likely to cause trouble later on.

Key electrically shorted

If you suspect that a key is shorted out, fix it by cleaning the contacts per Cleaning Keyboard Contacts. If this problem happens at the login prompt see Key shorted.

Liquid spilled on the keyboard

If water or watery liquid has been spilled on the keyboard (or if it was exposed to rain, heavy dew, or dampness) some (or all) keys may not work right. The dampness may cause a key to short out (like it was pressed down all the time) and you may see the screen fill up with that letter if auto-repeat is enabled. If it's gotten wet and then partially (or fully) dried out, certain keys may not work due to deposits on the contact surfaces. For the modern type of keyboard, one may readily take apart the plastic sheets inside and dry/clean them. For the old type one may let it dry out in the sun or oven (low temp.). When it's dry it may still need contact cleaner on some keys as explained below.

Cleaning keyboard contacts

Keyboards with membranes

On some newer keyboards, the plastic sheets (membranes) are easy to remove for inspection and cleaning if needed. You only need to remove several screws to take apart the keyboard and get to the sheets. On some old IBM keyboards the sheets can't be removed without breaking off many plastic tabs which will need to be repaired with glue to put back (probably not worthwhile to repair). Such a keyboard may sometimes be made to work by flexing, twisting, and/or pounding the assembly containing the plastic sheets.

Keyboards with individual switches

What follows is for older keyboards that have separate hard plastic switches for each key. Before going to all the work of cleaning electrical contacts first try turning the keyboard upside-down and working the bad keys. This may help dislodge dirt, especially if you press the key hard and fast to set up vibration. Pressing the key down and wiggling it from side to side, etc. often helps.

If this doesn't work, you may try to clean the key switch with a liquid contact cleaner (available at electronic supply stores) which usually comes in a spay can. To get to the switch, you first need to remove the key-cap (the square that you hit with your finger while typing). Warning: Key-caps on modern keyboards can't be removed. Often, the key-caps may be removed by prying them upward using a small screwdriver with the tip placed under a key while preventing excessive tilting with a finger. There exists a special tool known as keycap puller but you can get by without it. The key-cap may tilt a bit and wobble as it comes loose. It may even fly up and onto the floor.

Then you may have two choices on how to clean the contacts: Use contact cleaner spray directly on top of the key switch, or take the key switch apart and clean it (the best way if it comes apart easily). Still another choice is to replace the key switch with a new or used one but this is often more work (and more cost if you have to buy