It seems that the most recent Apple TV software update has rendered a lot of second and third-generation Apple TVs virtually unusable, with the set-top box device's Home screen displaying only the Computers, Music and Settings apps with no other channel options available.
According to a thread on Reddit, an Apple representative has confirmed that a fix for the bug will be included in a future software update for the Apple TV. Users can manually check if any new firmware update is available at any time through the Settings app.