Alexa not responding at all.

Alexa not responding at all.
My Alexa Echo Plus has stopped responding. I have reset using both the buttons at the top and the small reset button on the base, I have also deregistered on the app, all to no effect. Unit will go into set up mode, will run through the setup process and reconnect to my wi-fi but no response at the end of the set up - any ideas?

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