I've been using an Xbox 360. A family member of mine recently got an Xbox one and used the same xbox live account for both consoles, but when he changed the gamertag of the same account on the Xbox one, the 360 would not let me log into it. I have made my own xbox live account and have logged in. Somehow, I can access the games that were previously saved to the console but all the data saved on the hard drive is completely gone. Since it was saved to the console, I don't understand why it's all gone.