You first need to contact the landlord and let him or her know what happened about the blown fuse and your inability to get access to the fuse box to replace the fuse and restore electricity to the rented property.Most likely the landlord's locking of the access to where the fuse box is located in the rented property was an oversight. Once the situation for your call is explained to the landlord and your need to have a key to the area that is locked where the fuse box is located, he or she most likely will give you a copy of the key for future access to prevent a repeat of the inconvenience of having no electricity for a longer than anticipated period of time.