Can NOT change background WINDOWS 7

Hello,

No matter what I try, I am unable to change my background pic.... if I right click on my destop, the properties options does not pop up. I am able, however to change my screensaver and other things like that but not my wallpaper. when i right click on a pic it will not give me the option to save as a background unless Im online and when i do it online it still does not change my background. I have a compaq mini and im running windows 7... idk if that makes a differnce but its getting frustrating!!!!!