Did you check your tv settings? Is it possible the tv had an software update overnight and restored settings to default?

Does the Arc still play music? What tv do you have?

While there’s always the minute possibility of a failure of the Arc, there’s a much better chance of a failure in data transmission that should be checked before jumping to that conclusion.

So, a few things to do first. 
 

Unplug the Arc from power. 

Unplug the TV from power.

While they’re unplugged, check the HDMI cable by removing it from both ends, the TV and the Sonos, then re-seat that cable. You’re trying to ensure a good connection, make sure that it is seated firmly on both sides. If you have a spare cable, you could try a substitution here. 

Wait 5 minutes before plugging the TV in first, then the Sonos.

Check to ensure that the TV has CEC (or whatever your TV’s manufacturer calls it) turned on.

Watch a source, hopefully at this time everything is normal again. 

However, if it isn’t, it would be useful to know if the Arc is showing in your S2 controller. If it is, I would recommend that you submit a system diagnostic, 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.

I have fixed it.  I unplugged the power to everything and then plugged back in. Everything rebooted… the Samsung tv, the Sonos Arc, Comcast cable tc and Apple TV.  That reconnected them all. And everything is working. This strategy goes back to my software support days. First rule: Reboot. Thanks for your detailed answer. I had actually gone through that before restarting. The only thing that had changed over night was that Sonos did not let me do anything last night before I okayed a new agreement. It stopped my bedroom speaker as soon as I started it.