No input detected in Audacity despite showing in Control Panel

I’ve been using Audacity regularly to transcribe old cassette tapes. Suddenly, to-day, it won’t work: a complete flatline on recording. I’m using a RealTek sound card, and recording via the Line In, but the fault affects all inputs, including the microphone. So far as I am aware, there have been no hardware or software changes since it was last working.
Audacity is set to Audio Host = MME, Recording Device = Line In (RealTek High Definition…), Playback Device = Speakers (RealTek High Definition…)
I have been into Control Panel/Sound/Recording, and I can see the green bars by my input devices jumping up and down, so the signal is reaching the computer OK. I assume therefore that drivers are OK.
I have also been into RealTek HD Audio Manager. Using the Line In tab, I note that Recording Volume is unmuted, but Playback Volume is muted. If I unmute Playback Volume, I can hear the cassette tape sound from my loudspeakers (but Audacity still doesn’t see anything). So again, it seems that the hardware connections are made and drivers OK.
I was using Audacity 1.3.13 until this problem arose. I then downloaded and installed 2.3.1, but this has not changed anything. The OS is Windows 10, Version 1809; the update to 1809 took place 6 weeks ago and Audacity has been working fine since then. The Windows Update History shows minor updates to Microsoft apps 3 weeks ago but again Audacity has worked OK since they occurred.
Any advice would be much appreciated.

Well… That’s weird… Usually if the hardware works with Windows, it works with Audacity.

The only thing I can think of is, try a different host - WASAPI or DirectSound instead of MME.

Doug, thanks for your quick reply. Reassured that it “ought” to work, I checked that I still had the fault (I did), and that changing the Audio Host would not help (it didn’t). So I then did an uninstall of Audacity 2.3.1 and reinstalled it, this time resetting preferences. And it did work, so all is well.
Thinking back, I recall that when I did the original install of 2.3.1, I I had not yet done the uninstall of 1.3.13, so it is possible that twhen I did uninstall 1.3.13 it knocked out some component that the new version required. Certainly I got an odd error message the first time I ran 2.3.1, even though it appeared to have come up all right. That didn’t happen following the latest reinstall.
Moral for anyone facing the same issue that I was: try a clean install of the latest version, uninstalling your current version first, resetting preferences, and taking any error messages seriously.