Thanks for your continued help.
Here's a brief description of what happens when I follow your suggestions.
Right-clicking on the speaker icon in the lower-left corner of the screen and selecting Recording devices takes me here:
For each of the two devices I can then click on configure, which takes me to the next screen, where I select headset microphone:
Unfortunately, I don't seem to be getting any sound at all from either of the two options, i.e. the volume indicator
never moves an inch...
This is slightly odd, as I would have thought that one of these would be the inbuilt microphone, which I distinctly remember working some time ago... (possibly before I started updating all the drivers).
In terms of the properties of the two microphone devices. These show up, respectively, as:
and
So, on the surface at least, no red flags? Except nothing I say gets registered by either the headset microphone, or the inbuilt one... (this is both in the microphone test, as well as apps such as skype).
One more thing which may or may not be relevant: when I plug in the headset, no new microphone devices appear on the list, and none disappear, when I unplug it. Not sure whether this is what should be happening or not, but for info.
Thanks again for any further suggestions!
ps. When testing the microphone, I'm getting proper stereo sound through the headphones without a problem. So it's just the mic that seems to be malfunctioning...