From the computer:
Please go to Http://accounts.live.com (link may take you to a grouped page not found, so copy and paste it to your URL bar and go to that site, there is no WWW)
Sign in if prompted! On the Account Summary page please click on "Edit Security Info." On the next page please make sure you have at least 1 phone number, 1 alternate email, and an updated security question. if you're prompted to verify the changes please do so! **This will not work if you do not verify the updated email and/or phone number.**
Our next steps are from the Xbox 360 console:
From the Xbox dashbaord, please go to Settings > System > Storage > Hard Drive/Memory Unit > Profiles > Find your profile and delete it > Delete Profile ONLY (((very important, if you delete Profile and Items, those items are your saved games and avatar rewards)))
Clear your system cache a total of
1. Tap the Guide button on your controller, go to
Settings, and then select System Settings.
2. Select Storage or Memory.
3. Highlight any storage device, and then press Y on your controller.
Important Do not press the A button.
Note It doesn't matter which storage device you select, the cache is cleared for all storage devices.
4. Select Clear System Cache. (Do these steps 3 times or it does not work!)
Deleting the Marketplace Cache
Please go to Settings > System > Storage > Hard Drive/Memory Unit > System Items > Delete Marketplace System Data (It is possible for this file not to be there, that's fine as we would be deleting it any ways.)
Restart your Console
Next tap the Xbox Guide button on the center of the controller. This will take you to the Xbox guide menu. Select “Download Profile” and then after accepting to download your profile you will be prompted to enter your Microsoft Account email and password to recover your account. Enter in that information and your Gamertag to begin a fresh download from the Xbox Live Servers.
If your still getting a prompt to validate your security proofs then you did not validate your security proofs at Http://accounts.live.com and need to start the process all over after validating your proofs from the computer.