1. Select CTL-ALT-DEL and bring up Task Manager.
2. Choose File, New Task (Run).
(Do not includes quotes " " when enter commands)
3. Enter "CMD" and press Enter to open a Command Prompt Window.
4. Enter "CD \" and press Enter.
(This gets you to root directory)
5. Enter "CD \Windows\System32" and press Enter.
6. Enter "REM SHDOCVW.DLL SHDOCVW.OLD" and press Enter.
(Do a Google search on this file, but in short Show Doc View is what allows you to see the desktop, among other things)
7. Enter "COPY SHDOCVW.BAK SHDOCVW.DLL" and press Enter.
8. Enter "Exit" and press Enter to exit Command Prompt Window.
9. Reboot your system.
Possible causes would be a bad Windows update from MS.