Wallpaper issues, please try this steps

Click on Start, Run
2) Type REGEDIT and Press Enter
3) Click the plus signs(+) next to the following sections of the registry
HKEY_CURRENT_USER
Software
Microsoft
Windows
CurrentVersion
Policies
System
4) Look for the WALLPAPER key on the right hand side
5) Right-click and Delete this entry
6) Close the Registry Editor
Now try to change the desktop background.