Symptom
Typing numbers using the numeric keypad does not work, but the Key Caps utility indicates that the keys are being pressed. Holding down the Shift key allows the numeric keypad to work correctly.
Solution
1. Choose System Preferences from the Apple menu.
2. Choose Universal Access from the View menu.
3. Click the Mouse tab.
4. Turn off "Mouse Keys". If Mouse Keys is already off, turn it on and off again.
Note: Mouse Keys could be turned on inadvertently if certain programs (most notably games) make use of the Option key. Pressing Option five times in a row is the keyboard shortcut for turning on Mouse Keys. You can avoid this by deselecting the "Allow Universal Access Shortcuts" checkbox at the bottom of the Universal Access pane.