1998 Mercury Sable unable to unlock the car

If the key won't unlock either door, then you will need to get a tool called a "slim jim" to unlock it. It slides between the window glass and the weather stripping. Once it attaches to the lock assembly, you push or pull (whichever direction it needs to go to unlock) and it will unlock the door.

I live outside of Pittsburgh, and we can call the Police to do this for us or Tripple A will do it too. Most shops will have one in case they accidently lock the keys in the car.