itunes- can't send movie to Apple TV

Hello:

I'm new to Apple TV so please bear with me. I have a new Apple TV 3. Trying to send a mp4 video from itunes (on a Win 7 pc) to Apple TV. Keep getting an error message "an error occured while connecting to the Airplay device Apple TV. The network connection timed out". I can watch the movie through itunes on the pc, but can't send it to the ATV.

I have home sharing turned on and the latest software upgrade for the ATV and the latest version of itunes. I can send music and photos from the pc to ATV with no problem. I can also send the same movie from my iPad 3 to the ATV. When I select Computers on the ATV, I can see my libraries. I can watch youtube and trailers on the ATV so the internet connection is ok.

Does anyone have any suggestions? Many thanks for your help.