Wallpaper dilemma on windows7 starter?

i adjusted the screen resolution(with band master game open).
it went very slowly. then my netbook hanged, i can’t shut it down so i took off my battery. then i reopened it it was ok… then after the complete loading of the system my WALLPAPER changes to black… but all seems ok except for the wallpaper. when i change the wallpaper after closing the window i can see my wallpaper for 1 second then it turns black again… help me….