I have a weird Desktop background problem

Here it is.   I can't display my desktop pics/images.   It started when I was surfing and came across a pic that I wanted as my desktop background.  I "set the Pic as desktop background"  and then my images froze.  I can change my desktop color or my screensaver but I can't change the background pic.   Here's the other thing.  I can only see the desktop image during powering down.  Otherwise the desktop is blank except for the icons.