Got a new computer Loaded LR Copied back up from old computer and placed in LR folder in Pictures Open LR and opened catalog In Library all sub folders and pictures are listed However all pictures are only Gray no pic

Bought a New computer loaded  -  LR application--  appears to loaded ok.  Copied Backup from old computer Wanted to have pics on new computer   Saved Backup to LR folder in Pictures   When opening Catalog  all sub files and corresponding number of pictures are correct However all pictures are blank with gray color.  Need to understand what I have done wrong.