Ok, I've exausted everything I know of, read articles, searching this message base, etc...etc.., and I'm fed up trying to fix this problem. Thanks Winston for your help, but I cannot find any problems in the networking aspect of things on the MAC that could be causing this. I've given up on getting this to work and disconnected and boxed my Apple TV.
What in the world ever happened to the good ole days when all you had to do was just power up/connect a device made by Apple and everything just worked with very minimal effort in setup?
I had this same problem. Did every singlething everyone said (that I could understand). Apple TV and computer on same network, restart Apple TV, restart computer, make sure no firewall, look at settings on computer and ATV, etc Finally turned router off and on with no hope it would work but it did. Yay!