Audacity records, but the waveline is flat

Hello everyone. The other day l accidentally destroyed Audacity’s previous configuration file, and when l started the program again, it loaded the default, including the setting for automatic update. Thus l got the latest version without asking for it, and while l like some changes to the interfase Audacity at the same time stopped working at recording audio from me. It used to be as easy as pushing the Record button and starting a music track or playing a sound online. They would be captured in the waveline. I dont’t know what has happened - l am quite sure my previous configuration file had nothing special in it - but the waveline is flat now. Audacity records, but on playback l hear at most the ping of recording equipment.
Just in case l will mention that my playback and recording volumes are at 100% and that l have tried switching between MME and other recording and playing devices. Another user has written about what sounds like the same problem:

Could it be the interface? did you set your gain? I still have no idea how the flatline happened, but I’ve resolved it. I set the gain on my Vocaster two.

Audacity doesn’t do that. It will tell you a new version is available but you have to download it and install it manually.

What version are you running? Have you given this new version of Audacity permission to use the “microphone”.

From your description it suggests that you are recording sounds playing on the computer.