I have been careless in pressing buttons. Result is I have lost the setup on the left-hand side of the tracks (don't know what it is called) which allows the user to mute tracks etc.
Tried quitting the program, but crucial bit still missing. Even tried restarting the computer, but it seems to have decided that I want it to stay that way forever!
For use next time is there an "Oops button"? I tried Ctrl Z earlier, but no joy.
How to start again from scratch please - preferably short of uninstalling and re-installing!