I downloaded a group of photos to my computer and wanted to rename each photo. When I attempted to do so, I received a message saying "changing file name extension may make file unusable". When I did it, the photo disappeared. Why can I not change the name? I have done so in the past with no problem using a different camera.
Are you trying to Rename the files using Photoshop Album Starter Edition or simply from Windows Explorer. In either case, you should rename only the file name and leave the extension as it is. For example, if your file name is "file1.jpg" you should only change 'file1' and leave ".jpg" as it is. Otherwise, Windows will not be able to recognize the file as a picture file.