First you will have to create a short cut, for that open the notepad in your Windows 8 by pressing the Windows key on the desktop and then type Notepad on the start screen. When you will press Enter Notepad will open on your screen.
Copy the command mentioned below and save the file:
Make sure you save the file with the extension .scf, for instance you can name it as ShowDesktop.scf.
This shortcut is similar to the Show Desktop button that was present in the Quick Launch area on Windows XP.
Now in order to set the shortcut automatically, press Windows button on the desktop.
In the search bar type Schedule, in order to launch the Task bar Scheduler.
Click the Settings category that will take you towards another page.
Select Schedule tasks from the visible applications. You can also access Schedule task from the control Panel and then Administrative Tools.
Click on the Task Scheduler Library that is present in the list shown on the left side of the Task scheduler window .
On the right side of the same window right click on the pane and select Create New Task.
A new window will appear on your screen with few tabs. Click on the General tab and then type Show Desktop in front Name.
Next move into Trigger’s tab and set a new trigger with the help of New button.
From the options in the Begin the Task, select At Log On and then hit the Ok button.
A small window will open with the title New Action. Click the Action Tab and set the action at Start a Program.
Hit the Browser button and search for the shortcut folder created earlier.
Select the folder and hit OK button.
Next you will have to move towards the Conditions tab
Uncheck the “Start the task only if the computer is on AC power” checkbox.
In the end click Ok to save the changes made and take an exit from the window.