A few things to try:
1. Go to Control Panel \ Appearance \ Personalization. Click "Show hidden files and folders". It's right next to folder options, then check the box for "show hidden files, folder, and drives". Click Ok. Now, navigate to C:\Users\[YOUR_USERNAME]\ AppData\ Roaming\ Microsoft\ Windows\ Themes. If there's a wallpaper(s), delete it. If there's an .ini file, open it with Notepad and erase the contents. Reboot.