In the car, doors closed, ignition off, key in hand.
Press the central locking button (the one on the dash or near the handbrake, not the one on the key).
Doors should lock then unlock, immo light should stay on.
Within ten seconds, press the button on the key twice. The doors should lock then unlock.
Now try starting the car.
If this does not work, post again, there is a way of temporarily by-passing the immobiliser.
fred, December 2009