Desktop Background (Wallpaper) won't change.

I turn on my Dell XPS M1710 laptop and the desktop backgroun/wallpaper is all black. I can only change the solid colours, but when I want to change it to anything else under Picture Location, whether it be any Windows Wallpaper, Pictures, Sample Pictures, or Public Pictures it won't show up after double clicking it as it asks me to. What do I do?? I'm sick of seeing solid colours as my desktop background.