image of previews don't appear after importing files on catalogs

Files have  been correctly importated on catalog . But in the right side of the screen  , the images doesn't appear even if files of images are présent  ( xhne I click on a preview, the image appears on the central screen

when I Click on "G" , the files image appears on the central screen but the images them selves are not visible

I try to check the catalog , but nothing happens

Thank you for your help