I have an Imac and an apple TV and an Ipod Touch 4th Gen. I use a Toshiba LCD TV. I have a Motorola Surfboard Wireless Gateway Modem SGB900. After 6 hours of trying to setup my device I schedules an Express Lane call for this am. The Apple Tech recommended turning off my modem's firewall and to reconfigure my ports. I hardwired my computer to the modem via ethernet cable, pointed to the modem's ip address
http://192.168.100.1 and logged in with the default admin and pw motorola. Under the Firewall policy tab I selected custom and went to advanced settings. I then discovered that some of my ports did not accept inbound traffic. I wrote down the existing info carefully eg port name NTP, number 443:443 and protocol (TCP/UDP). I then deleted the port, and added it back with the same information, but this time checking the box allowing inbound traffic. you need to reset the DNS port, the Http port, Https port, NTP port (network time protocol)and DAAP (Itunes). I saved the settings, did a reset on the ATV and voila! It signed me in and I could connect to Itunes, Netflix etc. This method works for Motorola only, As that is the brand of modem I have, I surmise you might be able to use the same strategy if you are able to log into your router via IP address (same method when setting up a passkey for your hoe network. Sorry for such a long post. Im a newbie, and feel free to edit or redact as necessary. Thanks! see the following Apple articles for port settings: Six network ports are used by Apple TV for communications on your network.
TCP port 123 is used to communicate with a network time server.
TCP port 3689 is used to communicate with iTunes while using the iTunes Library Sharing feature.
UDP port 5353 is used by Apple TV for automatically finding computers with iTunes on your network using Bonjour.
TCP port 80 is used for communicating with podcast servers.
TCP port 80 and 443 are used for basic and secure communications with the iTunes Store via the Internet.
TCP port 53 is used for regular DNS.
Note: These ports may also used by other services like MobileMe, You Tube, and Flickr.
These are well-known ports used by Apple products, like iTunes. If you can use all the features of iTunes, these ports are likely already open on your firewall or NAT router.
For a list of well known Apple ports go to this article on the discussions forum:
Well known TCP and UDP ports used by Apple software products
Last Modified: December 07, 2010
Article: TS1629
Hope this helps!