I had some problem after installing new drivers for Nvidia. After having followed the instructions answered to this question, I now only have the Nouveau open-source driver. I can have access to my desktop, but I'm stuck with a 640x480 (4:3) resolution. No other resolution is proposed in the dropdown list of the "Displays" utility. I tried installing the two Nvidia drivers suggested in the "Additional Drivers" utility, but each one broke my display again. Now that I have reverted back to Nouveau again, what should I do to get a higher resolution ?