this is more than likely a loose connection, if one wire being a (-_ or (+) comes loose then the speaker wont work.
the panel on the door just clicks off but you will have to remove the door handles and window winder handle
when you have access to the speaker, unscrew the 3 bolts securing it to the door and inspect the rear of it for the + and - terminal and make sue they are both in tact.
if both are in tact and secure, redo the door card/handles becuse it will be a loose connection in your head unit (cd player)
an of chance and it is very slight is that the speaker could have blew
hope this has been a help to you,
S bence, October 2006