You have to go into preferences (either under iTunes or Edit depending on OS) and then select the Sharing tab. That should allow you to turn Home Sharing back on. If the other libraries are still not showing up go into "Advanced" and make sure that home sharing is on and that the account that is signed in is the same on all the computers. If not simply turn home sharing off and back on and sign in with that account. Also make sure all the computers in the house are authorized to actually play the music from that account.
Hopefully that is all you need to do. That fixed this issue on my home network.