sonos system doesn’t connect

Hard to tell, there’s not a lot of data in your post. First thing I’d check is to make sure that your radio/wifi is turned on, on your Arc. The Surrounds (your two Era 100s) and Sub connect to it via a ‘hidden’ 5 GHz channel. There is a secondary method, but for testing purposes, it’s better to use the original,  intended method. Once it’s working, we can make adjustments as needed. 

Next, I’d take a look at the way your Arc is connected to the TV. You should be using the supplied Sonos cable, connected at one end to the Arc, the other to the ARC/eARC HDMI port on your TV. Might be helpful to know who makes your TV, which model it is, and which port(s) you’re using. 

It could be the TV (or the source) that’s restricting the output to stereo. Might be worth checking the audio settings in the TV set, as well as anything that you’re using to feed it. If you were to tell us what all of these things are, and the settings are, we might be able to key in on something…or not.

I’d also make sure you’re testing with an Atmos or Dolby Digital signal. You won’t get anything from the surrounds and Sub when watching a stereo source, like many talking head shows, or old TV shows. 

Finally, I’d consider calling Sonos Support to discuss it.

When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system. They certainly have more access to data about your system that this community doesn’t.