Written by Joe AimonettiSome users may experience issues with their keyboards not working as expected--possibly due to the Mouse Keys function being enabled on their Mac. Read further to get a resolution to this issue.
If you find that you are unable to type letters or numbers on your keyboard, it is very possible the Mouse Keys function has been enabled. These symptoms may also exist if you log in to a user account on a Mac where a different user account has Mouse Keys enabled.
Mouse Keys can be enabled a number of different ways. The setting could have been activated while syncing from a MobileMe account that had the preference enabled, migrating a user from another computer using Migration Assistant that had the preference enabled, or by pressing the Option key five times (if that setting is enabled in System Preferences).
To check your System Preference settings, or to enable/disable Mouse Keys:
1. Open System Preferences and click on the Universal Access preference pane.Additional information provided in this Apple KB Article:
2. Click the Mouse & Trackpad settings tab.
3. Click the "Off" radio button next to Mouse Keys.
Note: You may also check/uncheck the box for "Press Option key five times to turn Mouse Keys on or off".
Note: If you are logged on to a user where Mouse Keys is already disabled, but your keyboard is not responding properly, toggle the radio buttons for Mouse Keys "On" then "Off" to restore normal functionality.
"When Mouse Keys is enabled with one of these keyboards, you can use the keys 7,8,9, U, I, O, J, K, L, M, and '.' (period) to control movement of the mouse pointer and mouse clicking, but other numbers, letters, and keys cannot be used. (Keyboards with no numeric keypad or Num Lock key include: Apple Wireless Keyboard (2007), the built-in keyboard on MacBook (Late 2007) or newer, MacBook Air, or MacBook Pro (Early 2008), or newer.)If you continue to experience issues with your keyboard keys not working properly, read this Apple KB Article for more resolutions.
The following keys will continue to operate normally when Mouse Keys is enabled: Esc, Function keys, Eject, Delete, Tab, Shift, fn, Control, Option, Command, and the arrow keys.
If you would like to control the mouse pointer with the keyboard and also use the keyboard for typing, enable "Press the Option key five times to turn Mouse Keys on or off" in Universal Access preferences. Then, press the Option key five times each time you want to switch between controlling the mouse pointer and typing."