Someone deleted the Show desktop button in the quick launch toolbar, here is the way to restore it:

1. Create a new text file
2. Put in the following content:

   [Shell]
   Command=2
   IconFile=explorer.exe,3
   [Taskbar]
   Command=ToggleDesktop

3. Safe the file as: Show Desktop.scf
4. Copy or move the file to your quick launch toolbar