if you get the beeping sound & the immobiliser won't let you enter the code, it's highly likely that you have at first entered the code incorrectly, thus, the car thinks it is being stolen.
to remedy this, take the keys out of the ignition, make sure that the handbrake & steering lock are applied. lock the car & give it about half an hour for it to reset itself.
hopefully, this should do the trick.
ryan g
September 2010