Instructions
Turn on your Xbox 360 and gain access to the dashboard. Move to the "My Xbox" option and then "System Settings." Select "Memory" and then "Profiles." Click on the profile that has the gamer zone set to "Cheater" and delete it from your dashboard.
Return to the "Memory" screen and delete all of the items in your "System Cache."
Press the large Xbox button in the middle of your controller. Select "Recover Gamertag" from the menu.
Enter your gamertag, email address and password details and select "Continue" to recover your gamertag. Do not sign into the account yet.
Turn off your 360 console. Turn the console back on and sign into your account. Insert a multiplayer game you play often into your disc tray. Start an online multiplayer game and then exit it right away.
Sign out of your account and then sign right back in. Your Gamer Zone will have changed from "Cheater" to "Normal."