If the elevator motor is DCV and it has its own generator for power, the generator has a timer that shuts it down after a period of non-use. Often time the generator will not start back up because the relay or vacuum tube is faulty. This is a common and easily identifiable problem. Any competent elevator mechanic would look there first. There are also Bldgs. with a panel in the lobby that may have key switches and related devices in it. Good luck.
