Are you sure the computer is outputting a signal on the HDMI connector? 

This may help too: 

I double checked HDMI in box with Sonos beam gen 2 with my PC monitor all ok, but with audio not working with setup that.  

From what I can tell, your board has an SPDIF output on the back, you can use optical cable with adapter included with Beam 2 instead of HDMI 

Yes, I used this solution. Check in Sounds, I see have signal sound dancing, but no heard any sound, all config is default but no sound. Do you have any comment for config this? Thanks.

Is there something you need to configure in settings, to send the audio to that port? 

The only thing I can say is:

• Make sure that Beam is using input as a source (Sometimes Airplaying, Spotify Connect can change a source. By replugging the connectors or switch to TV source in the app sound should be back)
• In Windows Make sure to use correct sound output (sometimes disabling other outputs is needed to get correct result)
• Make sure that both Windows and Beam have volume up (try increasing in manually on beam) 
  
  I’m no expert but those are the only tips that I can provide to help. 

Yes, I don’t know what setup needs to be set in Control Panel/Sound/...S/PDIF for beam gen 2 using optical out.

Most PC's do not do HDMI-ARC, but the Beam needs it. That's probably why you did not get sound from HDMI. Why optical does not work for you remains a mystery.

Yesterday, I tested again and have some results: 

• PC → Sonos HDMI → Monitor → OK => Sonos HDMI ok
• PC → Sonos HDMI + Sonos HDMI to optical → Beam gen 2 → no sound
• TV → Sonos HDMI + Sonos HDMI to optical → Beam gen 2 → no sound => I think Sonos HDMI to optical has a problem

Or HDMI port on Sonos beam gen 2 has problem.

Are you sure you’ve configured your pc to send a signal to that HDMI port? Or to the optical port?

What signal does the Sonos app report that it’s receiving?

Have you spoken with Sonos support to see if they have any suggestions?

Or your PC does not do HDMI-ARC and neither does the TV (or HDMI-CEC wasn’t turned on)?

I changed to use through optical base on mainboard, but no heard sound. :(

I’ll ask you again: 

What signal does the Sonos app report that it’s receiving?

Have you spoken with Sonos support to see if they have any suggestions?

• Yes, if I play with airplay it ok.
• No, I haven't spoken with Sonos support before. But I will try to contact them to ask about this

Still no answer to what does the app report it is playing? (When it is not working over optical).

• I don't understand the app report what does this mean, I try to see it all in the app but don’t see any log or report, Can you support or guide me? Thanks.
• Yes, I spoken with Sonos support before, but they told me: “While there may be a possibility to get audio via a computer with a Beam, we can not guarantee it or troubleshoot it as it was designed for TV audio, not PC audio., We can't exactly advise regarding a computer connection to the Beam as it was not designed to work with computers.”

In the Home Screen for your room containing the Beam, it will show the format of the video signal - DD5.1, DD2.0, etc. This will indicate whether the pc is sending any data to your Beam. What does it show? 
 

Also, to check: Do you get a video image using the pc optical connection? What if you plug the lead into your tv, so the pc sound and picture should play through the tv? 

If I'm not wrong try to check if your motherboard has Realtek hardware, which has no license for using driver for optical out. You need external usb card, if you use optical out from Asus motherboard, Realtek driver is to blame.

Use aaf Optimus audio tool. If you Google this you will find it.

Install the realtek drivers + 5.1 Dolby digital and dts. Reboot and it should work.

Now you have the drivers for audio over optical. And DTS 5.1 as well.