Access the icon modification dialog by right-clicking on your desktop and pressing "Personalize," then click on "Change Desktop Icons" from the pane on the left.
Select the 7 icon for which you wish to restore the default, then press the "Restore Default" button.
Press "Apply" then "OK" to save your changes and exit.
Restoring Default Folder Icons
Right-click on the folder you wish to restore the default icon for and press "Properties" from the context menu.
Open the "Customize" tab and click on the "Change Icon" button to access the icon-modification tool.
Press "Restore Defaults" to reset the icon to 7's default selection, then press "Apply" and "OK" to save your changes and exit.