If you accidentally or intentionally deleted the Show Desktop icon from the Quick Launch toolbar in Windows XP or Vista, try the following to restore it:

Click Start, Run and type the command:

regsvr32 /n /i:U shell32.dll

Sometimes you need to restart your computer for this to take effect.

If you previously had a broken Show desktop icon on the system tray, look for a new working one. You may need to expand the system tray (click on >>) to see it. Once you have it working icon again, delete the broken one by right-clicking on it an choosing delete.