Is this permanent or just happened now? Wait for a bit - they have a 'safety' feature on some of them that if you press the button too many times the mechanism has a bit of a breakdown and you need to leave it for a little while to catch up. If it's a long term thing then sound like the button is broken, as long as the lock mechanism still works when you use the key then I'd just leave it on a car that old, but maybe get in tough with the dealership.
