Re: Lenovo W520 > NVIDIA 2000M > External Monitor = Problems
How is your external display connected? Many laptops have the function key to switch between the laptop screen and the external VGA monitor. If it's an HDMI connection, it will depend on how that is connected in the laptop. It is possible I suppose that your external display is run through the optimus somehow, making it unusable if GPU switching is disabled. I hope this is not the case.
Again what type of connection are you using to your external display?