We have a 1999 Expedition; It appears that the battery strength is good although when I turn the key it makes a loud click and disables all power to the vehicle and will not turn over the engine or start. After several minutes I try the door locks and they work, turn the key and it appears that power is restored; turn the key the rest of the way to start it and I hear the loud noise again and all power is killed and the engine does not turn over. Any idea on what could cause this?