Display properties (Desktop) Help

Hello everyone,I recently went to my display properties to change my background,only to find out that it is corupted, well sort of,, I want to get it the way it used to be. Well you know how it has a little screen showing you what your curent background looks like well when you click on a bitmap image,, it does not display on tha little screen unless you click on apply thats the only way you will know what kind of bitmap it is I hope I explained it right,I have windows Xp Home edition,Service pack 2..Thank you...