I CAN NOT LOCK OR UNLOCK DOORS WITH KEYS OR REMOTE
SECURITY SYSTEM on 2000 Mercury Cougar
I have seen cases where the door lock cylinders will not work because of lack of use. If you have been using your remotes exclusively over the years the lock cylinder may need some lube to begin working again. Try spraying some lock cylinder graphite into the cylinder and work the key to see if the cylinder will turn. If that will get you in the car, great! If not you may need to call a lock smith or have your car towed to a repair shop. Once the door is open you can have the remote system diagnosed.