You probably just need to re-sync the key.
Turn on ignition (dash lights on, do not start engine).
Press button on key fob (you may have to press a few times before it works).
Doors should lock then unlock.
Ignition off, exit car, remote should work as normal.
The circuit boards in the key are not very strong.
If you have a recurring problem it could be a dry joint, the battery connection broken or you may have to put a small piece of card on top of the battery to hold the board down onto the buttons.
freddie
May 2009