This happens when you delete the /home/user/Desktop folder. To restore the normal desktop back, do following steps:
$ vi ~/.config/user-dirs.dirs
Change the line with XDG_DESKTOP_DIR = “$HOME” to XDG_DESKTOP_DIR = “$HOME/Desktop
After that, create the Desktop folder in your home directory using:
$ mkdir Desktop
Restart your computer and you should be able to see the normal desktop.