We're excited to announce that we've fully migrated the Xbox Forums to their new home, here on the Microsoft Community forums!
As of today, going to forums.xbox.com will redirect you here to the Xbox area of the Community forums. We've moved all of your existing threads over so you can continue and start conversations with the new forums experience.
We sincerely appreciate the feedback you have provided over this transition and can't wait for you to check out the new Xbox Forums!
On halo.xbox.com, your username and gamertag aren't linked. It's not like this website where it signs you into your gamertag to log in. It's possible that someone took your GT as their username. Although it's odd, since your GT is rather unique.
Please try using complete sentences when you post so we can understand what you're saying.
What do you mean by "it doesn't let you pick any?" You have to physically type in the username you desire. There is no list of names to choose from. If you can't get "Massamo" come up with a different username. Halo.xbox.com is not linked to you Xbox Live
account, so you can choose any username you so desire, unless it's already taken.