Laptop wallpaper keeps disappearing!?

Hey guys, for the past few weeks my laptop's (Asus UL50A Notebook) desktop wallpaper keeps disappearing. I'll put a picture on my background and some time later (a few days) the picture disappears and the the background goes blank with the Asus logo in the back (the original picture it brought when the computer was purchased) and the taskbar at the bottom goes on "auto-hide" mode. Both of these things happen at the same time. Any ideas as to what's happening? Oh and by the way, i've done several scans with my antivirus thinking it could have been some infection but nothing. Thanks!