Ullyses68, these forums work best when you create a new thread with a first post of your own, as the original poster's problem and solution, although similar, could be very different in detail. It's great that you're researching here, but the quickest path to a solution is your own thread. That being said:
This issue often is caused by missing proofs or other missing information in your Microsoft Account or Xbox account. I'd go to http://account.live.com and sign in there then click on Edit Security Info to make sure you have a cellphone number, an alternate email address and a security question/secret answer there. After you check that, please change your password.
Then, go to http://xbox.com and sign in there, click on My Account, then choose Billing Contact Information from the left side of the web page, and make sure all the information is up to date there.