On the project I’m working on at the moment the main toolbar has disappeared. I’ve been searching for it in order to add a footnote but I can’t find it. I started another project - well the same project but with a different name so I could keep writing but now I’ve got confused over which one is which. I’m in a muddle and where is my toolbar? 
Did you by any chance make the mistake of trying to navigate back and forth among documents using Alt+Left/Right Arrow? When I first started using Scrivener, I did that all the time, from habit in Web browsers and other programs that use this shortcut to go forward and backward. In Scrivener, the Format Bar (if this is the one you’re talking about) is toggled on and off with Alt+Right Arrow. I was constantly making it disappear, until I trained myself to use Scrivener’s navigation methods rather than this one that I was used to from other software.