Images showing hourglass means their thumbnail generation is still in progress. As an alternative, you can select the image with hourglass, right click on it and select Update Thumbnail. This would update its thumbnail.
Hi I have the same problem. The computer spends a while thinking about it, displays a ? for a bit and then still doesn't show the thumbnails. Any ideas? The programme doesn't suit my needs if it can't even display the photos. I haven't undertaken any changes so I don't know why this has started happening.