Suddenly having a problem with my 'Save As' navigation panel. Normally the window displays the typical navigation panel displaying the split screen and the main file names on the left, while the individual files are displayed in main part of the screen. The account I was working on in my main drive saves automatically, and then I save it down to an external backup drive. Now when I try to access my 'save as' navigation panel I get a mostly grayed out blank  screen with the only option to save my file as a new file on the desktop, or back up onto my main drive. I need to retrieve my original navigation panel  to carry on. How do I do that?