How do I turn the water back on in my house?

I am at my parents lakehouse and they turned the water off the last time they came here. I called them to ask how to turn it back on but they won't answer. There is a valve under the driveway so I bought a valve key and tried to turn the bolt and it turned but the water still isn't on. I know where the water meter is on the side of the house, but there is a lock on the box that doesn't have a keyhole so I'm not sure if that has anything to do with it but if anyone could tell me what to try to do I would be extremely grateful.