Desktop Audio

The PC sound worked perfectly until I connected an old Win 7 PC to the HDMI input on the back of the new Win 10 Pavilion. The sound from the old PC connected to the HDMI connector comes out of the new Pavilion, as does the picture. Works a treat. However, once I toggle back to Win 10 PC the sound no longer comes out of the Pavilion. I have to connect an external speak to the headphone jack to hear anything from the Pavilion on Win 10. 

If I switch back to the HDMI (Win 7 PC) input, the sound works via both the internal speakers and the external headphone connected speaker, without issue. If I then switch back to the Pavilion, I lose the internal speaker and can only hear via the external one.

It would appear that the internal audio switch for the internal speaker is somehow "locked" to the DHMI input, even if i disconnect the HDMI cable. There doesn't seem to be a way to get sound back out of the internal speakers in Win 10 on the Pavilion.

Now, interestingly enough, if I boot to Bios, I can run the sound test on the pavilion and the internal speaker works a treat, even if the HDMI cable from my old PC is connected or not. So the Pavilion is working as expected, but somewhere Win 10 thinks the sound should be coming from the HDMI input, whether it's connected or not.

I need a solution to this, and I expect there's a setting somewhere that I can force the audio back to the internal speaker by overriding a setting that has become confused.

Any help would be greatly appreciated.