How can I fix my desktop?

I recently changed of desktop wallpaper (I picked a new one from the Windows free pictures, like the one I had before). My system is Vista. When I boot my computer all goes well both the wallpaper and the desktop icons show up and work without problem. BUT, if my computer goes to sleep, when I wake it up, the icons are gone and the wallpaper stands alone like frozen (if I right click my mouse trying to change something - anything...nothing happens) and so I have to shutdown the computer to regain accessibility.