Is it the infra red type remote? If so you can check it is working by pointing the key at the lens of a switched on digital camera or camera phone. Watch the camera screen and push the lock button on the remote. If you see a flash on the screen, the key is working, if not replace the battery and try again.
If it's working you may have to re-synchronise the key to the car.
Press down the central locking button (it's either by the handbrake or on the dash) and hold it for at least five seconds.
The doors should lock and unlock and the immobiliser light should come on.
Within fifteen seconds point the key at the receiver and push the remote button once. the doors should lock and unlock and you should now be able to start the car.
If this does not work you may have an immobiliser fault. You will need the immobiliser bypass code, which should be with your cars documents. Post back here if you dont have it, it can be worked out.
Brian.J.
August 2008