I recently had trouble with my Nvidia GTX760 recognizing one of two identical monitors, both of which worked fine with a Macbook Air and DisplayLink USB adapter. The Ubuntu default Nouveau driver wouldn’t find the monitor at all, while the Nvidia 331 driver would only allow 640×480 or 800×600 resolution. Eventually I found the display log was reporting an issue obtaining the EDID, a small packet of data reported by monitors describing their capabilities (make, model, resolution, etc).
/var/log/Xorg.0.log ... [ 11972.301] (**) NVIDIA(0): Unable to read EDID for display device DFP-3 ...
Since I had an identical monitor I was able to force the system to use that EDID. 
With /etc/X11/xorg.conf saved to the disk, a CustomEDID option can be added.
/etc/X11/xorg.conf
...
Section "Monitor"
...
Option "CustomEDID" "DFP-3:/home/matt/hardware/acer-v226hql-edid.bin"
EndSection
...
Section "Screen"
...
SubSection "Display"
Depth 24
Option "CustomEDID" "DFP-3:/home/matt/hardware/acer-v226hql-edid.bin"
EndSubSection
EndSection
If it’s not fixed upon reboot, check if the xorg.conf file was renamed. There’s currently a bug, and a workaround, but hopefully that’s resolved soon.
Matt Williamson 