By default, Windows 7 hidden and disabled the “Quick Launch”, "Show Desktop" is just the one of quick launch.
1: Right click mouse over task bar, Select “ToolBars”, and then "New toolbar…"
2: Input the following path line to the Folder textbox:
%userprofile%\AppData\Roaming\Microsoft\Internet Explorer\Quick Launch
3: Click “Select Folder”, then you will see there is a "Quick Launch" item came out on the taskbar, maybe on the right bottom corner, “Show desktop” is just there too!