What version of Aperture are you using? Its always been the case that you cant view anything just by clicking on the Library item in the Aperture sidebar. In Aperture 2 there's an option (a child of the Library) called 'All photos'I can't now remember if that was also there in 1.5 (which I can't now open because I've upgraded my library). Aperture 2 certainly introduced the 'All Projects' item, which shows all your projects arranged by a grid, each one represented by a thumbnail.