Displayport does not work when docking

[gazi666]

I am using the dock which is a gift from Lenovo when I bought my T400s. Today, I tried to extend the display to an external monitor through DisplayPort. It works when my notebook is not attached to the dock. But the screen of the external monitor turns black if I attach the notebook to the dock. My dock does not provide DisplayPort, does that mean I can only extend the display when it is not docking?

Second problem. Even it is not docking, clicking any options in menu of Fn+F7, a dialog box pops up saying it cannot detect any external monitor. Then I use Windows built-in display configuration to set my external monitor to work.

Final problem. If I set boot screen as DisplayPort in BIOS, the external monitor gets the control at the beginning (the notebook screen is black), when Windows Vista displays the login screen, the notebook monitor gets back the control (the external monitor is black). After logon, both monitor can show the desktop. The switching of control is quite weird I think.

Thanks for any help.