Does your apartment have its own hot water tank and/or furnace? If so then they must be on their own breakers.
Also, have you tested every outlet? As Badger says there may well be one designated for a high draw unit like an AC, that would account for another one of the breakers that you think is unused. Try flipping all four of those off and leaving the main breaker for the outlets and lights on, then go round and plug something into each outlet in turn and see if there's one that doesn't work. If there is, leave your test device plugged in and flip each of the four breakers in turn until the outlet comes on.
Or, y'know, call the freaking landlord.