I just bought a 2000 Mercury sable. When pressing the lock/unlock buttons on the door or remote, doors do not lock or unlock. The motors or relays sound like the doors locked or unlocked, but they do not actually lock.

Any ideas or suggestions?

Are you hearing 2 sets of noises or just 1 set? Does it sound like its trying to lock then unlocks?
That is a 2 step process.

Just one.

The only real way to tell then is to open the door panel up and see what is going on. If it were 2 sounds then you would be checking for something else.