I have a Dell desktop Optiplex 790. I recently started having a problem with dual monitor viewing. The problem is as follows: I have a graphics card (nVidia) as well as a built in display port and VGA output into the motherboard. I'm using a HDMI connection from monitor 1 to my nVidia graphics card and everything works fine. However, if I connect monitor 2 to either the display port (using a cable converter) or VGA output I get "No Signal" on the monitor. If I reboot, then only monitor 2 (the one connected to display port) will turn on, however the coloring scheme would be terrible. It is running something like a 16 bit color Windows scheme and the picture looks very distorted. However, if I boot into safe mode then the normal coloring scheme displays just fine. It seems that it will not run the display port and graphics card simultaneously. This is very strange since this was running just fine for the past 6 months....I also replaced the motherboard but the described above problem still occurs.
I'm running Windows 7 Professional. And it's not a problem with the monitors nor the cables.
When I look up the Optiplex 790 on dells website, the onboard video from intel is listed as A07, I really dont think this means anything though.. can you uninstall your current onboard video drivers and then try installing the drivers again?