I also now have this problem, the game crashed whilst reloading after i died on a segment in Thessia, so i restarted and it locked my entire xbox when loading up. It now locks repeatedly either when i load the game with my GT signed in, or if i load the game without a GT signed in or another one it will load fine, then lock as soon as i try to sign my GT in. Every, single, time.
I've done everything possible to try and clear it, deleted off all DLC, removed the save game, cleared the HDD cache, deleted and redownloaded my profile, and tried every variation of the above. Still the game will not load. I must admit i am rather frustrated to say the least having played through the first two several times over and wanting to complete the whole story arc. I guess thats what i get for saying that i would be surprised if Bioware managed to leave in a game breaking bug to a mate literally the day before, i mean its not like they are Bethesda, i expect it from them, but not Bioware. I hope a patch for this comes soon.