Symptoms

• If you are unable to type letters, numbers, or symbols, you may have Mouse Keys enabled on a keyboard that has no numeric keypad or Num Lock key.
• If you log in as a different Mac OS X user (who does not have Mouse Keys enabled) while the keyboard is in this state, you will be able to type numbers using some keys, but you will be unable to type letters.

Resolution

Mouse Keys may have been enabled through the Universal Access pane of System Preferences or by pressing the Option key five times (if this setting is enabled in Universal Access preferences in System Preferences).  If you are using a new computer and have never enabled Mouse Keys, you may have used Setup Assistant or Migration Assistant to migrate a user from another system which had Mouse Keys enabled, or you may have used MobileMe to sync the preference for Mouse Keys from another computer.

1) Choose System Preferences from the Apple menu.

2) Choose Universal Access from the View menu.

3) Click the Mouse tab.

4) Click Off, next to Mouse Keys.  If you have already logged in as a different user where Mouse Keys is disabled, click On and then click Off next to Mouse Keys, to return the keyboard to normal operation.

Additional Information

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.)

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.