Here is the trouble shooting article
One other solution i found was
You can use the ethernet connection between your Apple TV and Computer.
If HomeSharing works this way it is an issue with your wifi
Here is the troubleshooting article for WiFi
Apologies if you have already tried all of these
If you connect the Apple TV via ethernet rather than wifi is there anything showing?
If not the issue is not with your wifi. If yes then Wifi is the issue.
I found that when i upgraded to itunes 11, I had to turn off all the homesharing on my computers, Devices and Apple TV.
I then re enabled it and it worked fine.