can't find library

hi, ive been using my atv fine. i have now changed internet provider which shouldnt matter, and added another atv. i can now watch stuff through netflix on atv so must have internet connection but when looking for my library it just says turn on home sharing? i have tryed this all different ways but nothing seems to change this it cant find my library???? please somebody help????? this is using a atv3

the other thing i dont seem to be able to do is mirroring from macbook pro to atv which i could do before????