No desktop wallpaper

Hello,
i been having this problem for almost 4 months.my desktop wallpaper will no longer appear,even when i tried to changed it many times..but sometimes it would only appear on my desktop everytime i changed it..but when i turned off the computer and open again it will suddenly disappear..how will i fix this?can you please give me an option or any idea of how to fix this wallpaper problem?ill be looking forward to your response...thanks everyone...