content of audio drop down menus disappeared

I have been using Audacity 2.1.1 on Windows 10 with great success recording youtube clips. All of a sudden, two of the drop down menus are blank and say (when I hover with mouse) “No recording device” and 'No recording channels".
Audio host MME and Playback device “Speakers/Headphones Realtek” are not affected. This means I cannot record or playback direct from my computer as I have done previously. This is a mystery to me. Please help. Thankyou

Audacity can only use the recording devices that Windows presents. If no recording devices are available in Windows then Audacity does not show any recording devices for MME and Windows DirectSound hosts.

Did you install some software that changes audio devices, such as Skype?

Was there a Windows Update recently that tried to update your audio drivers?

What you can do is open Windows Sound and follow the instructions there to show and enable disconnected and disabled recording devices.

Assuming you have copyright holders’ permission to record the YouTube videos concerned, then you don’t actually need any recording devices showing in Windows Sound in order to record YouTube playback. Change the Audio Host in Device Toolbar to Windows WASAPI then you will have (loopback) recording devices for each of your playback devices. Choose “Speakers/Headphones Realtek” as your Audacity playback device then choose “Speakers/Headphones Realtek (loopback)” as the Audacity recording device. See Windows WASAPI loopback recording - it applies to Windows 10 too.