Apple TV sees my computer but will not access the librabry

I have been trying without success to get my apple TV to view/Access my ITunes library on a media PC via Home Sharing, for some reason the Apple TV sees the library Name within "Computers", but when I select it it goes off and says its loading, but then errors with "Could not Connect to "Media Library", "Make sure the computer is on the same network as your apple TV, ITunes is upto date and running" after 2 mins or so

I have tried creating a new user on the PC and setting up a new ITunes instance but have had the same issue

Both the Apple TV and PC are connected via the Ethernet connection on my Virgin Router, and presumably as it can see the computer they must be communicating happily between the two, I have also got a Mac with ITunes on it, and the apple TV communicates happily with this, although I wanted to use the PC as its always on and would enable access from the Apple TV at all times, rather than having to turn the MAC on, and also free disk space Is far greater on the PC

Any help would be gratefully appreciated as this is driving me insane !

Thanks

James