I am trying to add an external monitor to my Dell XPS 17 L702x. It has an Nvidia 550 card with Optimus. When I received the laptop, I immediately wiped the OS and installed Windows 7 Ultimate. It took some time to get all the drivers installed and I had some issues with Optimus but I believe everything is correct at this point.
I tried using an HDMI cable first. The external monitor was recognized by windows 7, Nvidia and the on board Intel card. For all intensive purposes, the monitor was connected and working. However, there was nothing being displayed on the external monitor. I was able to switch to using the external monitor as my primary, the mouse dissapeared on the second screen and the resolution, brand and location of the second monitor were recognized. But there was nothing displayed. The external monitor screen was black and the monitor was sleeping.
I tried re-booting with the monitor connected. I tried turning the monitor off and on. I tried extending and cloneing the desktop. No change.
I tried again with a DP connector that converted to VGA and I had the same problem.
I also tried with a DP connector, converting to DVI and it worked just fine without issue.
So as it stands now, I cannot see anything displayed on the external monitor with VGA and HDMI but have no problem with a DVI.