Transfer IPhone 11 photos to computer

I have transferred my IPhone 11 photos to my computer many times; however, when I attempted to transfer them on the last two occasions, I got a message stating that, "no videos or pictures could be located." I have many photos to be uploaded. Initially, I will get a green bar, indicating that the photos are being transfered, but after a few seconds, the aforementioned message about not finding any photos appears, even though the green bar is still running behind the message. I let it run for a hour, but no success. Help, please. Thank you.