Vista - desktop problems

My computer recently encountered a problem and had to shut down. When it came
back up, the picture that I had as my wallpaper was no longer there. I
clicked on the desktop link to change my desktop image, and it will not let
me. The list of all of the options is there, but I am not able to click on
any of them, and the "browse" button is not even available. The only option I
am given is to choose a color for my desktop. Why can I no longer add or
change my wallpaper? Can anyone help me with this?