Thumbnails show onething, click and another photo appears?????

I shot a job and a few photos were missing?

I usually load to a folder from windows explorer. Then I load thumbnails into

photoshop and edit. Several photos were not there. I could not find them.

Then by accident, when I maximized a thumbnail, instead of closing it and

clicking on the next one, I used the back key, and there was my missing photo.

The thumnail shows one photo, but when you click on it to open in windows

explorer to see it, another photo opens up. How could this be? What caused

it? How do I get the thumbnail to match the photo I need. How do I prevent it

from happening again?

Thanks,

Abe