landrover discovery?

My key fob started to take ages to turn alarm off , then wouldnt work at all , and my car wouldnt start - immobilised- i changed the battery still didnt work. I went through the instructions in handbook ( turning key in car door with security code )managed to start engine and drive car but as soon as i turn the engine off it immobilises again- It does allow me to program in the code each time

Jackie
January 2010