I have resolved the problem, but not completely.
It seems to me that the kernel is not loading the proper module for the nvidia driver. What I did was the following:
cd /lib/modules/`uname -r`/kernel/drivers/video/
sax2 -r 0=nvidia
Everything was running fine. The only problem that I have now is that whenever I restart the computer the old kernel module is being loaded into the kernel and I have to redo all the commands above in order to start the session.
How can I make the new module to be loaded on every reboot?