extend displays latitude E6520

I have a problem with my Latidude E6520 , about the possibilty to setting multiple displays

I use a docking station and I have  connect at these two monitor one a VGA port and second monitor DVI port , after I have changed the display settinf at the voice " extend these dysplays" but unfortunately do not work , I don't see in my two monitor connected the extended of my desktop , only one monitor connect work the other don't have nothing signal

does someone have had the same problem?