Check, if Aperture has opened the correct library. Launch Aperture with the alt/options key held down to see the library chooser panel and select a different library.
If your Aperture library on a drive not formatted for mac? Then Aperture may not be able to pen your library any longer and you need to relocate the library to a different drive formatted Max OS X Extended Journaled.
If you look at the library in the Finder, is the size still correct? Or has the library become much smaller?
If the size of the Aperture Library.aplibrary is still large enough, your image files will still be in the package.
Have you checked, if any filters are set in the search fields in the Browser and Vierwer?
So all your photos are probably still inside the library - good.
Have you tried to repair the library or to rebuild it? I'd try all three library first aid options , if you have not already done so. Check, if your backup of the library is current before trying to rebuild.
See the paragraph: "Use the Aperture Library First Aid tools" in this document: http://support.apple.com/kb/HT3805
it appears that the library that I can not see but listed in first aid indicates 55,000 versions and 741 originals. somehow I need to make it show me the versions, which I expect to be my pics. an advice.
tried to repair but the default library is the original one set in the subdirecotry for aperture. unless I will move the older upgraded library to this location I dont know how to force it to rebuild the library, if this is needed.
perhaps some setting in aperture will allow me to see the versions?