My desktop wired mouse deletes images and videos when I left double-click. How to fix?

This started happening about a month ago. Before that, double-clicking on an image or video opened the file in the appropriate program, just like it would open a folder or a text file. It still does the latter, but deletes images and videos - but not into the Recycle Bin. These files become hidden in their current folder, and can be retrieved with an undelete program, but that is getting to be a nuisance. I can, of course, right-click on an image or video icon and open it in a selected program, but I don't always remember to do that, so I temporarily lose the file. The Mouse Properties in the Control Panel (Windows XP SP3) doesn't make any reference to the related mouse button properties. Any ideas?