In rare occurrences, people have found that some keys or keystrokes on their systems do not seem to be working properly. This may happen in certain software situations, indicating a configuration error, but it also may happen because of hardware malfunctions. If you experience problems with a specific character not working on your Mac, try the following set of possible fixes.
Hardware vs. software
If you are experiencing input issues with your keyboard, the first thing you should do is determine whether the problem is hardware-based or software-based. To do this, the best tool to use is the keyboard viewer, which will show what keystrokes have been passed to OS X from the input device.
If you do not have the viewer available in the input menu, go to the "Language & Text" system preferences (called "International" in versions of OS X prior to Snow Leopard) and check the option to enable the Input menu in the menu bar. Then check the option for the Keyboard viewer so it will appear in this menu, and choose it from the menu so the viewer displays (it will stay on top of other windows).
With the viewer open, press the keys that are not working to see if they get highlighted in the viewer. If they do not, and other keys work fine, then you likely have a problem with your keyboard.
Over time keyboards can wear out, either with the button actuator under the keycap going bad, or the hinge mechanisms getting stuck or broken. Sometimes people will abuse their keyboards in frustration only to have the effects of this abuse show up later on. More commonly, people will spill liquids that can stick keyboards together.
If your keyboard is physically broken then the best course of action is to get a new one; however, if your keyboard is gummed up with grime or spilled liquid then one option before replacing it would be to give it a thorough cleaning. This can be done with alcohol, toothpicks, tissue, and Q-Tips, but some people have mentioned having success with using a dishwasher. If you would like to do this, first read our article on.
Beyond the keyboard itself malfunctioning, there are several options in OS X that may prevent some keys from working. If you have inadvertently bound a key combination to a possible keyboard shortcut, then you can override some of the built-in options for that key combination. For instance, if you create a custom shortcut using Command-X in the "Keyboard" system preferences, then using Command-X may no longer cut selected items.
The system should not bind a single character (or the same character with only the "Shift" modifier key held down), but there is a possibility that an error could cause this to happen. They user-defined keyboard options are available for editing in the "Keyboard" system preferences; however, they are stored in the hidden global preferences file for the user so you might try removing this file to have the system recreate it.
To remove this file, run the following command in the Terminal:
Keep in mind that doing this will also revert some other user settings to the defaults, including the system fonts and sizes, view options for text, some window resizing and scrolling behaviors, text substitution, and mouse speeds. These can be set up again in the system preferences, but may require you to take time locating and adjusting them to suit your needs.
Besides key combinations, some other system services may also use customized key combinations and thereby prevent the key from being used in other features. The most common of these is the built-in Text-to-Speech option where you can set a key to activate the system's speaking of selected text or the entire text in a document. Unlike the standard keyboard preferences, character keys can be set for this function without the use of modifier keys.
To check for this option, go to the "Speech" system preferences and choose the "Text to Speech" tab. Then if you have the option checked for speaking when a key is pressed, you can either uncheck it or click the "Set Key..." button to change it to another key combination. Similar to the Text-to-Speech option, third-party applications may also have similar hot key features so you should check any you have installed to see if they are reserving a key sequence globally for any functions.