My home sharing will not work! have tried everything. Same password a few rooms apart and they will not see each other?? Any ideas great fully received.

I recently bought an Apple TV which we love. We have a huge iteunes library - films, music etc. Would love to stream it to the appleTV - As directed - turned on home sharing on apple TV and main computer - a few rooms away. They will not see ecb other. I have re-typed in the passwords - re-booted both the apple TV and computer. Nothing seems to work. Both say home sharinf=g is on - but in main computer menu on appletTv screen - says it cannot see anything. Please help.