If you accidentally delete the Show Desktop icon from the Quick Launch toolbar, here’s how to get it back:
1. Open Notepad
2. Type these lines, precisely, into Notepad:

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

3. Save the file on your desktop as “Show Desktop.scf”
You see a new icon on your desktop that looks remarkably like the Show Desktop icon that used to be on your Quick Launch toolbar.
4. Right-click the new icon on your desktop and drag it to the Quick Launch toolbar.
5. Drop the icon wherever you like on the Quick Launch toolbar and choose Move Here. If you choose Move Here, Windows automatically deletes the icon from the desktop.

If there is no icon in Quick Launch toolbar then you won’t be able to move the above way. In that case browse to
“C:\Documents and Settings\Username\Application Data\Microsoft\Internet Explorer\Quick Launch”
Here “Username” is your windows login name. This folder is hidden so just copy above path substituting username and paste it in Windows Explorer adress bar. Press enter and folder will open. Now copy or move the “Show Desktop.scf” to this folder. It will immediately appear in Quick Launch toolbar.