Welcome to the Apple Community.
If your problem persists get yourself a micro USB cable (sold separately), you can restore your Apple TV from iTunes:
- Remove ALL cables from Apple TV. (if you don't you will not see Apple TV in the iTunes Source list)
- Connect the micro USB cable to the Apple TV and to your computer.
- Reconnect the power cable (only for Apple TV 3)
- Open iTunes.
- Select your Apple TV in the Devices list, and then click Restore.
(You may already have a micro USB cable if you have a camera or other digital device)
I just wanted to say that unplugging the ATV from the power source for 30 minutes (not seconds) worked for me. I found the solution on another thread and it seems to be the solution for a few people.