1.  Enable Quick Launch.   If the Quick Launch feature is disabled, the desktop icon will not
     appear on your taskbar. Right-click your taskbar, select "Properties" and select the check
     box next to "Quick Launch." Click "Apply." 

2.  Check the Quick Launch section of the taskbar to determine if the desktop icon is restored.
     Use your mouse to expand the Quick Launch bar (showing all the icons). 

To Manually Restore the Desktop after the above:
1. Open your Notepad program and enter the following text exactly as it appears:

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

2.  Save the file as "Desktop," "Show Desktop" or "My Desktop." Enter the file extension
     as ".scf" and save it to your desktop.

3.  Expand the Quick Launch bar and drag the "scf" file onto the taskbar. The original desktop
     icon will be restored.


Read more: How to Get My Desktop Icon Back on My Task Bar | eHow.com