Keynote Conundrum

After spending days learning Keynote basics to create a presentation I now can not for the life of me open the files to view/finesse edit them. I can surely see the finished product but the video, effects etc are not there when I 'preview' the files. Frustrating and in need of your expertise as all I get is Unable to open “Portfolio.key” because it isn't a valid Keynote document. I'm on a Mac PC and it has Keynote 9 ver 5.1.1. if that helps at all. Thanks in advance.