I'm trying to fix a problem with a computer system and I'm not sure where to go next. My office manager said that her numeric keypad wasn't working, though the keyboard was otherwise fine. I replaced her keyboard but to no effect: the new keyboard worked fine except for the numeric keypad. On further investigation the keypad works normally when num lock is off, acting as arrow keys, but when num lock is on I don't get anything. The computer is running Windows XP. Any ideas of what might be wrong?