You should post in the hardware forum, where more are likely to see it.
I have an hp tx2000 laptop with an Nvidia 6 series graphics card and when I try and hook up my external monitor so that the display is only on it, the monitor (Insignia NS-LCD22-09) displays an error that the VGA mode is not supported. I only get this error when I try to use it as my only display. I can have mirrored monitors or extended desktop just fine. I have the latest Nvidia drivers installed and have the refresh rate at 60 hertz with a resolution of 1680x1200 , which is what the monitor (TV) is designed for.