HDMI Output Problem

I have a Dell 660 with Realtek High Definition Audio running Windows 10. I have an HDMI connection to a Sony STR-DN1030. The Sony receiver is curently identified in Device Manager as a software device. It is also identified in Control Panel/Devices as a play device.

Sound works through headphones. No sound to the receiver. When I open Dell Audio or Sound, the HDMI output is not an option, not visible.

Also, the TV connected to the receiver is not recognized as a display device.

The problem did not coincide with the installation of Windows 10. It worked under Windows 8. It  work initially under Windows 10. But now....