AppleTV does not respond white light blinks slowly

If you see a continuously flashing status light, that indicates a failure to start up properly. If the cold restart didn’t improve it, then the system software may need to be re-installed. Unfortunately, for the 4K model, users can’t do this themselves. Instead, contact Apple Support for assistance.

Restore your Apple TV - Apple Support

If you have an Apple TV 4K

If you […] see a black screen on your TV and flashing indicator light on the front of your Apple TV, contact Apple Support.

Try removing power from your AppleTV for a few minutes and then plug it back. First rule of troubleshooting electronics.