These are instructions on how to put your Apple TV 2G into DFU mode.
Connect your Apple TV to the power outlet and to your computer via a Micro-USB cable.or
Hold down the Menu and Down buttons on your remote for about six seconds until the light on the device begins to blink rapidly.
Let go of both buttons then press and hold the Menu and Play buttons together for another six seconds, then release.
iTunes will then detect the device in DFU mode.