Help — Photos stuck - spinning wheel.

My faithful photos app has a problem. When I start the app I get a blank photos window and the spinning wheel. I have opened photos from a different account without error. I have tried restarting and rebuild library, but after a few hours the progress is fixed at 5%.

Can I have advice at what to do? Is there something I can delete that may be causing the trouble? Should I just wait however long it takes for photos to repair itself? Is there a clever trick that will fix everything instantaneously?

Thanks for any advice.