Hi duvenhage
Lets give it a try 
First please post your computer specs. Open a terminal (Ctrl+Alt+t) and enter..
Code:
inxi -b
And whats xrandr have to say about all this?
Code:
xrandr
There is a GUI tool in your menu (System>Preferences>Hardware>Display). Have you tried this?
There is also the nvidia settings tool (System>Administration>Nvidia).
Give both a try if you haven't already.
That above link will not work for updates, just the most recent install.