I am using a Dell Latitude E6520 running Windows 7.  Currently, I have the laptop on a dock.  I keep the lid closed and  have two external monitors.  One monitor is VGA.  The other is the white digital connection (DVI? Sorry I do not know the technical term).  I would like to add a third screen other than my laptop screen.  If I am already using the VGA connection on the dock, can I also use the VGA connection on the side of the laptop itself to add a third monitor using VGA?  Or, would I be able to get an HDMI - VGA adapter and use the HDMI port on the laptop to connect a third monitor?