My 1996 300D traditional key is not unlocking/locking the doors. I changed both batteries in the key and the mirror was replaced a few years ago.

The green or red lights on the mirror stopped flashing. I am unable to lock/unlock the car directly with the key at the drivers side door. I place key in the key hole and turn key but door locks did not move.

Is there a chip in the key that requires a match with door lock for security purposes? Do I need a new key? Where can I start to diagnose?

Thanks for the guidance as I am not able to lock car at all.