I'm running an Nvidia k2000m graphics card in a Dell Precision m4700 lap top with 32gb Ram.   It uses Optimus technology to switch between an Intel GPU and the Nvidia GPU.  

In the preview device selection, Vegas doesn't recognise the graphics card.  So I can't select and external monitor.  The GPU acceleration aspect is working and Vegas recognises the card there but not in the external preview monitor dialogue box.   It just lists Windows graphics card without any options to select an external monitor.  I have tried switching Optimus off in the Bios but still Vegas won't see the video gpu and list external monitors.

I have installed the latest Nvidia Drivers and Intel drivers and windows updates.

The system works fine with Adobe Premiere and the external monitor works without issues.