LOCK UR DESKTOP 
this trick will lock ur desktop 
TRICK 1: First create a new shortcut on your desktop using a right mouse click 
and enter 'rundll32.exe user32.dll,LockWorkStation' in the location field. Name the shortcut what ever u want to like abc. Then just double click on it and your computer will be instantly locked 
TRICK 2: The Windows key + L also does the same thing 
AND THEN TO UNLOCK CLICK ON UR ACCOUNT NAME.....