No more black terminals after starting X!!!!
I have solved my problem with black terminals (i.e. Ctrl+Alt+F1) after X starts. All I did was to set to 0 the NVreg_UseVBios nvidia kernel module parameter. On my distro (Gentoo) I modified /etc/modprobe.d/nvidia and rebooted.
Hope this can help others who have the same problem!
EDIT: I forgot to say that I'm using 177.78 but I think the version doesn't matter
you can see if the parameter is setted correctly by cat'ing /proc/driver/nvidia/registry