If the Apple TV doesn't respond to remote commands, it may be due to a low battery, the remote may be un-paired, or it may be due to a software glitch. 

Low Battery

Your remote's battery may be out of power. Plug a lightning cable into the port at the front narrow end of the remote to charge it with an AC adapter. 

Remote Is Un-Paired

Hold the remote three inches from the Apple TV and press the 'menu' and 'volume up' buttons simultaneously to re-pair the remote with the Apple TV. 

You may be asked to place the remote on top of the Apple TV. 

Software Glitch

Unplug the Apple TV's power cord, wait six seconds, and plug it back in to restart the device.