I had this same problem for about a month. Eventually power went brown at only our building. I called BEL and they came by in about 20 minutes. They found that the service connection near the weather head was corroded. They cut the connection, cut the bad ends of the wire, reconnected, and that fixed the problem. If the problem continues and it's only your building (can even be multiple meters) then I would give them a call. It's their side of the feed so it's no cost to you.