First, to determine if your Link is unresponsive, please try charging your Link using a new USB cable or outlet.
If your Link is still unresponsive, it is likely that your Link is in a bricked state (can't turn the Link OFF or ON). It needs a hard reset. To reset the device, the battery needs to drain fully. Please leave Link unplugged for approximately 24 hours. Once completely drained plug the Link back in and it should be fully functional.
If this does not fix the issue, please reach out to firstname.lastname@example.org for additional support.