XPS 8700, Logitech HD Pro C920 microphone not working

Might help if you tell us exactly what you have tried so we don't suggest the same things again. :Idea:

Do you know if the webcam microphone works on another PC?

Is there an option for a Line In Mic in Control Panel>Hardware and Sound>Manage Audio Devices>Recording... that needs to be disabled?

Did you try reinstalling the Logitech webcam driver and software?

You say some application is muting the microphone. Try this: go to All Settings, type 'Speech, inking, & typing privacy settings' in the 'Find a setting' window at the top, in the 'Speech, inking, & typing' window click on Microphone on the left, then in the 'Microphone' window under 'Choose apps that can use your microphone' turn off the apps you don't want the microphone to use. Hopefully the app that mutes the microphone will be one of those.

I am surprised the number of apps that can use the microphone; my list has 13 apps.

Sorry I haven't replied yet. Just got back to computer. Don't have time to try your suggestions now, but I will try them when I've got more time. I'll let you know my results.

Have tried many things. Went to Recording Devices: unmuted, set volume to 50, 60, ...100. Every time I come back to it, it's muted again. I hve let Cortana 'Set up microphone', doesn't work.  I've disabled Line In. I'll try most any advice, even if what I've tried is suggested again.

Don't have another computer to hook webcam up to.

And scan thoroughly  for malware while you're at it...

Cortana thinks you are unfathful with Siri or Bixby.

There is a system preference in windows that says what devices are "allowed" to use camera and microphone.

Privacy settings also override this.

these issues occur if your microphone isn’t set as default or if it’s disabled, and here’s a way how can you quickly enable your microphone ...

1. Make sure your microphone is connected to your computer.
2. Right click the volume icon in the bottom right of the screen and select Recording devices.
3. Click on empty space in the window and then click on Show disconnected devices and Show disabled devices.  Under Right Click Recording Properties Set the Mic as Default Device and NOT disabled.
4. To check if your microphone is enabled select Microphone and click on Properties, and you’ll be able to see if it’s enabled or not.

The other issue can be that SKYPE is wresting Control of the device away and there is a conflict because Skype starts every time.  in Windows 10 speech recognition settings. It needs to be set to your audio device that the Mic is attached to. To stop Speech Recognition, say, “Stop listening” or click the Microphone button on the Speech Recognition control panel. To start the Speech Recognition feature again, click the Microphone button on the Speech Recognition control panel.

For best results it is recommended that you:
1. Select and configure your microphone
2. Train your computer to recognize your speech
3. Configure Windows Speech Recognition to start when you log in

Configure Windows Speech Recognition to start when you log in

Search for “Speech Recognition” in the Start menu
Underneath the “Settings” header, select “Speech Recognition.”
Activate “Advanced Speech Options”
In the “User Settings” section, ensure that “Run Speech Recognition at startup” is checked
Activate the “Apply” button

I've also scanned for malware/viruses etc. Did a complete computer scan. No issues. Tried the Speech recognition wizard, it didn't help. I've also done this: Search for “Speech Recognition” in the Start menu
Underneath the “Settings” header, select “Speech Recognition.”
Activate “Advanced Speech Options”
In the “User Settings” section, ensure that “Run Speech Recognition at startup” is checked
Activate the “Apply” button

Run Speech activation at startup was already selected. As was "Enable Voice activation".

Well, I've tried everything suggested here. Microphone (in my webcam) still keeps being muted. 'Set up microphone' program doesn't fix it. I speak the sentence provided and can see there is no 'volume'. My Webcam is listed as the Default Device in Sound/Recording.  When I go into the Microphone Properties, I see the Mic. is muted, Volume at 0. I manually change it, then sit and watch it. Within 30 seconds, it's changed to muted, volume 0. "Apply" box at bottom is greyed out, so I can't save my manual changes.

Maybe it's time to post on the Logitech forum?

And a quick Google search shows lots of peeps have mic problems with this exact webcam and Win 10, like this one, that says, quote: "...DELL AUDIO kept muting the microphone...".

Unfortunately, there's no solution because the OP said, quote: "...has suddenly gone away and the webcam microphone is working perfectly."  :Ick:

EDIT: Kinda farfetched, but did you try updating the audio driver? And what about uninstalling the webcam driver/software and reinstalling with its Compatibility Mode set to Win 7?

And anything here that you haven't already tried?

How to fix auto muting microphone on Windows 10?

Windows 10: Microphone Mutes Itself

Thanks for all the help Ron, and others here! I'll try these 'fixes' later today. Will also try the Webcam on a friends computer. Maybe it just won't work any more on mine. Or maybe it will just 'fix' itself some time soon. Just won't be able to Skype or talk to Cortana for now.

What would happen if you  connected a stand-alone mic to the mic port on rear of the PC?

If you don't have one and can't borrow one, you might be able to pick up a cheapie for a few bucks at places like Walmart, etc. just to see if that might be a work-around...

I was thinking about doing that Ron (getting a stand alone mic.). Have tried about everything else, except trying the webcam on another computer.