Apple TV can’t always be detected by Mac & iPhone

The crucial issue is the speed of your router. Ideally you'd have the Apple TV connected to a router via an Ethernet cable using Gigabit Ethernet (1000/baseT) and your router would have WiFi N, not Wifi G (which is slower by a factor of about five), for the iPhone connection. Then you'd want to make sure that the WiFi N router was operating on a channel not subject to interference from other routers nearby, or from physical interference that would lead to signal attenuation.

It would be a good idea to try putting your WiFi router in the same room as your Apple TV and your iPhone and to see if video image quality improves. If so, this is an indication that you were experiencing WiFi signal attenuation due to interference caused by the materials used in the walls of the building.

Also, if this is the first time you've used an AppleTV, and the first time you've tried to watch HD video streaming over the Internet on your television, it may be that your Internet connection speed from your Internet service provider simply isn't fast enough to support HD video. If you have DSL, you may wish to consider upgrading to a cable modem or fiber-optic service with higher bandwidth. This year I found that AT&T had made their Uverse fiber-optic service available in my neighborhood. I upgraded to Uverse and got Internet service at four times the speed of my old AT&T DSL service for the same price I was paying for the slower DSL.

It's hard to say for sure, but I'm guessing there was a problem with the network discovery service. Apple uses Bonjour to advertise various network services (iTunes sharing, file sharing, AirPlay support) without the need to manually input configuration data. Unfortunately it can be a bit prickly at times, so if somewhere along the way the "Hey, I'm an Apple TV" message got lost, didn't get sent or received by your iPhone or Mac, it won't show up as an available device.

Unfortunately, the way Bonjour broadcasts the data seems to be a bit temperamental at times. I'm not aware of any real fix, but a restart almost always seems to fix it. If you're on a Mac, you can try restarting the daemon responsible by running the following two commands in Terminal:

• sudo launchctl unload /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist
• sudo launchctl load /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist

But that will only fix things if the problem is the Mac not receiving the messages properly - if it's on the Apple TV's end, then restarting that is the best fix.