So, my ASUS laptop has an nvidia GT 650M . I have had this laptop since 2013 and I have been able to use dual monitors with the nvidia proprietary drivers, through optimus (prime).
I wanted to hook up my laptop to a second monitor again and for some reason the nvidia driver cannot handle the two monitors (though sometimes it works fine(ish) with mirrored screens). I have tried a range of driver from 340 to 358 and the result has been the same. It stretches the screen to span both monitors and the image does not correspond to where the mouse should be.
One surprising thing is that the nouveau drivers seem to handle things just fine, with a slight performance loss. I wanted to get full performance out of my GPU so I wanted to have the nvidia drivers working.
The laptop is running unity on both 14.04 and 15.10. The handling of the monitors also seems fine in lightDM but as soon as I log into unity the whole thing goes south.
I also tried starting the computer with the second monitor already plugged in and nothing seems to make a difference.
Any help would be appreciated.