Audacity does not recognise the tape player

I am using Windows 10 and the latest version of Audacity. The story is:

I have been using Audacity for some years and even a few weeks ago it worked fine.

Then a few days ago I tried to convert a tape to MP3 using it and it just won’t do it. All the functions work normally except that one; I installed a new version; checked all the preferences; checked the cables; restarted Audacity; cleaned out the PC etc etc etc to no avail.

I cannot see where the issue lies except there may be a missing option in the pull-down menu for the microphone recording. Or there is just something that is just not picking up the signal from the tape player (which is working).

Can you suggest a solution please?

Thanking you in advance.