Apologies for getting years mixed up with versions.
20 was flashing on and off when I posted but is OK now and have used it to edit and crop.
21 now flashing on and off so I can't use the crop tool to find out if there is still a problem
I am using a PC and I don't think there is a force quit option as there is on my Mac. I cannot close Photoshop by using any of the buttons or close window option so I have to close the computer and restart