Show desktop button is very usefull botton on the Quick launch toolbar. IF you press once it bring you the desktop to you and all open application is minimized and if you click it again all application is restore and you get your open application in front of you.
If the file accidentally corrupt or deleted, you can re-created or Restore it you can find the Show Desktop.scf file at blow path %UserProfile%\Application Data\microsoft\Internet Explorer\Quick Launch\show Desktop.scf
1) Restore the show desktop.scr file :- just open the other user profile and copy the
Show Desktop.scf and paste the file to above mention path. or
2)Re-create the Show Desktop.scf file:-
a) Start Notepad, and write blow lines :-
[Shell]
Command=2
IconFile=explorer.exe,3
[Taskbar]
Command=ToggleDesktop
b) open file menu, select the save button and save it to %user Profile%\Application Data\Microsoft\Internet Explorer\Quick Launch folder you must give the file name is Show Desktop.scf
Note :- it is for Windows xp and windows 2003 server.