somehow, all of a sudden, the trimmer window shows just the audio track. When I play the clip the trimmer window correctly shows the usual split-window (video playing on the top and the audio track appears below it). But once the clip finishes playing, the audio track appears again, filling the window so I cannot see and edit the clip. You might think I just need to drag a divider up or down to show both video & audio track but nowhere can I find such a divider - help

What a fool I am! A simple right-click shows I needed to select "Show video frames". Now it's all ok