Inside the page library, folders, and consequently the pages within them, are not visible.

Inside the page library, folders, and consequently the pages within them, are not visible.  However, we know the following:

• The folders are there, with pages included. We know this because everything shows up correctly in designer.
• The problem is related to the folders, because if we change the settings of the view to show all pages without folders, they show up
• One night everything was visible, and the next it was not.