There is a Show Desktop shorcut when I use Windows XP or Vista, but I can’t find it in Windows 7 and 8.
Show Desktop was a feature present in Windows XP and Windows Vista, but has been changed to the Aero Peek/Show Desktop button on the bottom right corner of the screen, near the Notification Area in Windows 7 and Windows 8.
The solution can be found here. I would recommend Option 1 as it is faster and easier, and the file doesn’t contain virus.
Hope this helps