profile has been tmpered with can not proceed.

i logged on this morning made a new car. then my garage went blank and my xbox locked up. now i can not sign in says i have been tampered with, pleasse help

Contact Xbox Live Support according to which console you’re using: http://support.xbox.com/en-US/

If it is a tampered profile, they can guide you through deleting that local profile and retrieving it correctly from Xbox Live.