dual head not works

I have a two output display in my toshiba Satellite (P100): a DVI and a VGA. So, I can use two external displays when running Windows.
BUT, when running Linux, the DVI output is completely ignored and the Nvidia-settings do not recognize the monitor connected in the DVI port.
I want to disable the notebook display and only use the two external display.
NVidia-settings do not recognize the monitor, but tells me that the first output is a LVDS type.
Hummm, how can I force to recognize the DVI port and ignore the laptop display?
By the way, I believe this is not a xorg.conf problem because the DVI monitor do not provide any signal. The FN+F5 keys doesnt work at Linux.

thanks for any hint.