I have a dual monitor setup, on
Ubuntu 15.10, with LightDM. Both monitors connected by HDMI, one connected to my NVidia GPU, and the other connected to my integrated graphics card. I recently ran into a few problems, after my internet connection was interrupted during a software update: I booted my computer, to which I arrived at boot noise, and no display manager started. I managed to get this fixed, after attempting many hacks and re-installations.
However, that beings said, I now only have one monitor which functions. I stress that it worked before this unfortunate ordeal. It has worked twice, both times with a freshly installed driver.
I tried installing NVidia Driver 352, which works, but doesn't detect the other monitor at all, and I have tried re-installing the Nouveau driver. The Nouveau driver detects the second monitor, and I am able to drag my mouse (which I can no longer see, at this point) onto the screen, and use the invisible sidebar; however, there is no visible output to the monitor.
The monitor which works, is the one which is connected to the GPU.
I have noticed that after my computer goes into sleep mode, and I wake it back up, by logging in, the second monitor turns on.
EDIT: I have found a non-permanent fix to my problem. By going into suspend/sleep mode, as I found originally, my other monitor would wake up. Therefore, I have created a keyboard shortcut, which calls:
xset dpms force suspend. This does the trick, but must be done every time I turn on my computer.