Try this:
* Open Navigator (F5)
* This should show the Navigator, with a list of slides, but no objects
  in the slides (or at least, only named objects).
* Click on the far right tool button (with "Show Shapes" as the tooltip)
* This should open a drop down menu with the options "Named shapes" and
  "All shapes"
* Select "All shapes"
* Now the list of slides should have small plus signs next to them, and
  expanding them should show all drawing objects in the slide.
* I'll note that neither right-clicking nor double-clicking them
  actually does anything, but at least you can see that they are there.
This seems far easier, and is, I think, what you want to know. Although
if it doesn't show everything, Tom's way will be more complete.
If you find things you aren't sure about, you may have to make a copy
of the file, and go through the copy, deleting or naming everything,
until you find the offending item or items, but if you're first going
to all that trouble, Navigator isn't really necessary in the first
place, so I guess a feature request should be filed to give a
right-click menu to Navigator allowing at the very least a "bring to
front" option.
Paul