Locked.If you want to win a rank, check out the Twitter @cubecraftgames - or check out the build competitions that are hosted (it ends today, so you're a little late).
If you don't have a credit card, and if that's the reason you cannot get a rank, try going to your local store and buy a Pay-Safe Card. This is similar to a gift card - you put a designated amount of money on it, and it allows you to buy from many stores - including CubeCraft.