Impossible to record a second track

Version 2.3.3; Windows 10.
After years of using Audacity, no problems, my PC crashed. After it was restored, Audacity works fine on one track only. Any attempt to record on a second track results in an error signal. It is even not possible to paste a previous Audacity recording (even a section of the first track) to a second track.

Do we know why it crashed? Windows 10 doesn’t just up and crash for no reason. It would be good to know what got that bad.