If your Apple TV has stopped showing up under the Devices heading in iTunes’ sidebar, there are a few things to check.
I can tell you for certain that growling at it doesn’t work (and yes, I’ve tried). Here’s the Apple TV fixit list:
1. Make sure that you’re using the latest versions of the Apple TV and iTunes software.
2. Is the Apple TV able to talk to the world? Ask it to play a trailer or Internet radio station to ensure that it’s communicating over the network. Likewise, make sure your Mac can also connect to the outside and other devices on your network.
3. On the Apple TV look at Settings -> Computers. Is the Apple TV linked to the Mac you expect it to be synced to?
4. Are your Apple TV and Mac on the same network?
5. Run Software Update (look under the Apple menu for Software Update) and see if there’s a Bonjour update available to you. The Bonjour Update 2010-001 has been known to reestablish a severed Apple TV/Mac relationship.
6. On the Apple TV, choose Settings -> Computers, select your linked Mac, press the remote’s Play/Pause button, and in the Disconnect From iTunes Screen choose Continue and press Play/Pause. You have just told Apple TV to forget about your Mac.
Open iTunes’ Preferences and select Apple TV. If your Apple TV appears here, select it and choose Remove Apple TV. iTunes has now forgotten your Apple TV.
Return to the Apple TV, choose Settings -> Computers, select Connect to iTunes, note the five-digit code, zimber back to your Mac, select the Apple TV under the Devices heading (assuming it’s there), enter those same five digits, name the Apple TV, and click OK. The Apple TV should now appear in iTunes’ Preferences and your Mac’s name should appear in the Computers screen on the Apple TV.
7. No? Drat. Unplug the sucker (the Apple TV being the specific “sucker” I refer to). Plug it back in to restart the Apple TV (at the same time making it more cooperative).
8. Still no? On the Apple TV choose Settings -> General -> Reset Settings -> Factory Restore. This takes your Apple TV back to ground zero. Every bit of media on it will be erased and it will revert to the software version that came with it. Once it reboots you’ll likely have to update its software. Hopefully, when you do that, it and iTunes will see eye-to-eye.
9. What, still no!? Sheesh…. Try reinstalling iTunes.
10. Okay, so…huh!??? Oh for the love of…
Growl loudly and count the days until the Boxee Box is available.