I am very sorry to hear that. I'm dreading the day my Audios start to fail.
First thing, try a different power-block and cord. They are standard Micro-USB so you can use any other ones.
If that doesn't work, try Factory Resetting your Audio.
https://support.google.com/chromecast/answer/6279415
If THAT doesn't work, there is really nothing else you can do. The unit must have failed. There is no way to get it repaired. There are still some old ones for sale on sites like eBay but the prices are insane.
