Its says this
0) If any of these steps to do on a PC or Mac shows you a message about a Blocked Account, please follow the onscreen instructions to Unblock it.
1) Go to http://account.live.com and sign in then go to Edit Security
Info. Is all data there up to date? (If not, please update it).
2) Go to http://xbox.com/accounts to click on Billing Contact Information
at low left and sign in. Is all data there up to date? (If not, please update it).
3) Go to http://commerce.microsoft.com and sign in then review
the payment info. If there's an out-of-date card or PayPal account, please add a new payment method then delete the old one.
4) Back to the console; can you sign in there now?
http://support.xbox.com/billing-and-subscriptions/account-security/security-proofs has more detail on this.
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