I can't access my Home Sharing libraries

I have tried so many times to find the shared libraries, and looked at all the advice so far. I have a windows, with the newest iTunes, 10.5, and am trying to connect my new mac to it, same iTunes 10.5. The boxes are ticked, the network is fine, there is no blocking firewall, both computers are authorised. I have also re-installed and re-started my computers numerous times. My old windows computer has connected to other computers before. After I sign in to home sharing and click done, it disappears. Where you go to tick the boxes, under preferences/sharing, it says "On, no users connected". its the same on both machines but they are on the same account. How come? and how can I get to share my libraries across computers? If i cant then i bought this very expensive new laptop for nothing.