My Aperture 3 library has vanished

HELP! This morning I imported photos and videos from my camera into my Aperture 3 library.  Everything imported OK. I closed the app before lunch and when I went back, everthing is gone: new import and alI the rest of my library.  I tried all three steps of the Aperture library First Aid. The steps seem to run OK but my library still isn't showing up.  When I open the "show contents" folder from Finder, the MASTER folder is empty.  I can't beleive I just lost all my photos.... Please help! 
PS I am running on a Macbook air with OS X Lion 10.7.3.


are you sure you are viewing the right Aperture Library? The name of the library you are viewing is displayed in the upper left corner of the window.
If it is not the correct library, go to the Aperture menu bar, press "File -> Switch to Library" and look at the drop down menu, if you see your correct library and switch to that.
If you are viewing the correct library, then maybe your images are hidden: Look at the search fields in the Browser and the Library Inspector, if any search rules are set; if yes, clear the search fields.