Audacity doesn't record my voice on new track

windows 10 Home, Audacity 3.0.3
I have imported an mp3 file and I see the two tracks and they play well. I create a new mono track, starting playing and then press R or Shift+R. Nothing gets recorded in the new track. But if not playing the music tracks I start singing and press Record, voice is recorded but the moment I pause singing, voice recording stops. I can’t record my voice in the new track when music tracks are playing.