My Apple TV (3rd generation) is not working. The light is on and blinking constantly. Can you tell me what is the problem?

If a cold restart doesn’t fix it, then you may need to restore the system software. Restore your Apple TV - Apple Support

Note the requirements for powering during the restore, and that the USB cable must support data transfer (not just charging).

Please try unplugging it from power for about 2 minutes and then replug it in and test it.