wallpaper disappearance on laptop

Hi I have had my laptop for over a year and never had a problem like this before. I have read the other forum but the advice given would not or did not help. My custom made wallpaper for my laptop always disappears if i shut down, log off, or even bring a window up for more than like 3 minutes. I have a up - to - date antivirus system (AVG) and there are no bad viruses anymore i even complety redid my computer (backed files to disks, wiped hardrive, and reinstalled windows) but it still disappears. Does any1 have any suggestions? :-\