The default LED function for most of our devices is to have the LED on constantly for the first 24 hours after a reboot, and then the LED will remain off with the exception of 4 seconds every 60 seconds, when it will flash on with the appropriate color for it's current status.
If we can be sure the LED is not flashing on at all, but is indeed off all of the time, we'd want to try a different power source and cable, preferably swapping with a device that is currently working, to be sure it isn't the source or the cable that is an issue.
If the different power source and cable do not help, you'll want to submit a technical support case for an RMA. The case will need to include the serial number of the defective device, the shipping address we should use to send the replacement device to you, and written confirmation from you in that case description or a case comment that there is no physical damage to the device we are replacing for you. Please also note the troubleshooting steps you've taken to avoid any repeat questions from support. You can reference this post if you'd like in the case to avoid overlap.
