Couple of things to check. First, make sure your Google Chromecast is still sending an optical signal. Pull the optical cable from the Beam, and check to see that there’s still a red light shining out from the end. Then double check the settings on your devices to make sure they’re still sending a Dolby Digital signal, and not something else, like Dolby Digital Plus, or Dolby Atmos, which can’t be carried across an optical cable. 

Then, if all that pans out, try playing some streaming music from the Sonos controller, to make sure the speaker is still working properly. 

Finally, after all that, I would recommend that you submit a system diagnostic within 10 minutes of recreating this problem, and call Sonos Support to discuss it.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your Sonos system and network.

Thanks.  No red light on the optical chord.  Why would that go out.  Once plugged in, I haven’t touched anything on the unit for 18 months.

To be clear: the red light should be on the end of a cord coming from the Chromecast, or indeed from the switch. 

PS...I’m using this switch:
https://smile.amazon.com/gp/product/B07JDGBBXF/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I tried connecting the HDMI input at sonos into switch output: nothing

I tried a new hdmi chord: nothing

New HDMI with optical converter: no red light. 

Is my HDMI input on Sonos dead?

red dot on the chromecast, i don’t know what you mean. its a hdmi chord.  where would the redline be on the chromecast or it’s chord?

It’s possible that the adapter (HDMI ARC to optical) is broken, although that’s the first time I’ve heard of such a thing occurring. What happened when you contacted Sonos Support?

It’s still important to make sure that the signal being carried across HDMI and optical is Dolby Digital, and not something more. 

There are no lights included in HDMI plugs and jacks. The TOSLINK source should emit a red light when active.

BEAM must be connected to an HDMI ARC or eARC port or TOSLINK through the adaptor. Regular HDMI will not work. Your switch does not support HDMI ARC or eARC. You could attach BEAM to a TV’s eARC port.

I suspect that the audio extractor in the switch has an issue. Mother nature is never fair, things break at the most awkward moment.

I was thinking of the Chromecast Audio. In your case you’d be looking for a red light on the end of an optical lead plugged into your switch/extractor box.