moving old Calibre files to a newer version of Calibre

I had an older version of Calibre (.8) running on Ubuntu 10.04, PC died managed to save Library folder, but now I can't seem to get any of the files into the new version of Calibre (2.55) short of using the "add books" button. Sorry if this has been answered, but I can't seem to find if it is

Thanks
Steve