Photos not linked

Hi there

I am having lots of problems with my Photoshop Elements 15 and I am hoping somebody will be able to help

Firstly, on my old catalogue, there are loads of missing thumbnails even though the files exist and I have tried to update/repair the catalogue. When I double-click the thumbnail, no large photo is shown. This applies to missing/blank thumbnails and "correct" thumbnails.

I have tried to create a whole new catalogue, and when I do this, it finds all my photos, creates correct thumbnails for them all, but again when I double-click each thumbnail, no large photo is shown

Please can you help as I am getting really frustrated, and am worried that I have lost all my tags on my old catalogue which I have taken years to create

Many thanks