Try deleting the Desktop .plist.
You need to look in your user Library/Preferences for the .plist. Hold down the option key while using the Finder "Go To Folder" command. Enter ~`/Library. Delete the .plist(s) for the application.
If you prefer to make your user library permanently visible, use the Terminal command found below. It does work with Mountain Lion:
You might want to bookmark the command. I had to use it again after I installed 10.8.2. I have also been informed that if you drag the user library to Finder it will remain visible.