No Images For Background Allowed

I want to change my desktop background, but when I go to OPTIONS, the images available are grayed out.? It it totally frozen. I cannot even put a theme in, the icons show up, but nothing else.I used to be able to change my background at will, putting photos I had taken up, but now when I go to those options, the only thing I can do is change the background color as the images (including the BROWSE button) are grayed out. I have tried just about every imaginable combination of modifying themes and choosing backgrounds, but still, the only thing I can do is change the color of the desktop. However, when I go to shut down the computer, the image I previously had selected shows briefly.