The problem is that I am no longer able to boot in compatibility mode for just turning on my Nvidia graphics to install the driver. Because no login screen will appear if Ubuntu is loading.
In Ubuntu 11.10 I was able to activate nvidia graphics only' option this way:
1) Change BIOS to 'compatibility mode' which will turn off the Intel card.
2) Install the Nvidia proprietary driver using Ubuntu's driver finder (Additional Drivers) and then reboot.
I was not interested using only the Intel graphics, for the sake of battery life. Now I have both cards running and they drain my battery life dramatically. And the main problem of this configuration no OpenGL is available, so I can't play any games any more.
At this point, I have a pre-solution. I uninstalled the nvidia drivers and installed bumblebee. Now the Intel card is recognized. I would prefer to run just the nvidia card as in Ubuntu 11.10 but for now this is better than nothing. Does anybody else have the same problem?