Central Locking System working on all but one door. Remote Central locking not working too!

I just got a Nissan Maxima 2004 3.5 SE from a previous owner. I noticed the following problems with the central locking system.

1. The key only locks/unlocks 3 of the doors by inserting it through the driver side door. The front passenger door remains unlocked in any case and can only be opened from inside using the inside door knob. The outside door knob cannot open the door.

2. The key fob cannot operate the central locking system remotely even after battery replacement. Though the red security light keep blinking every 30 secs as it should be.

Pls what could be the problem?/?