Make my wpf application Full Screen (Cover taskbar and title bar of window)

You need to set the ResizeMode to NoResize and WindowState to Maximized

  <Window ...    
    ResizeMode="NoResize" WindowState="Maximized">

You need to set the WindowStyle to none as well as WindowState to Maximized

<Window ...    
 WindowStyle="None"   
 WindowState="Maximized">