I was on vaction and asked one of my friends (non xbox-live member) to watch our dogs so we gave him a key to our house. I have auto-sign in so he got on my acc and apparently thought i would be happy that he figured out how to mod my gamerscore. He thought i would be happy because i got all the achievements and a high gamerscore. So now I can't earn achievements for games I did legit. He ruined my gamerscore and I don't know what to do. So what do I do?