Lightroom Main Display is frozen on the first pic in the folder

This problem started when I made an attempt to start a client shoot tethered to my laptop. I might have inadvertently done this incorrectly or pressed an incorrect button. Now, photos can be loaded into a folder, but the main display will not move beyond the first picture, even when another picture is highlighted in the lower tray. The secondary display seems to work in LOupe view, but this isn't adequate for my needs. How do I solve this problem?

Thanks.

Bob Cullen