Previews disappeared

I'm a bit frantic here. Editing a large portrait project, using favorites folders for the different people, I added a folder for one guy whose files were already in the Capture folder, and suddenly all my preview images disappeared, leaving a frame with a question mark and the message "Deleted, moved, or not accessible". Everything is stall there in folders in desktop, and rating stars are there also.
There must be a way to relink these, but I haven't found it. Do I need to start all over?