Oi Éderson beleza, bom vamos ver o que no que posso te ajudar pois ainda estou aprendendo mas tenho a mesma placa que você e sempre depois de instalar o driver da nvidia deva este problema como meu monitor o que fazia era reiniciar no modo seguro (recovery mode) ele vai iniciar com o driver vesa se não me engano aí corrijo a configuração pelo nvidia-settings e gravo o xorg para mim sempre resolveu e se for de ajuda segue o meu xorg só que meu monitor e CRT de 17.
# xorg.conf (X.Org X Window System server configuration file)
#
# This file was generated by dexconf, the Debian X Configuration tool, using
# values from the debconf database.
#
# Edit this file with caution, and see the xorg.conf manual page.
# (Type "man xorg.conf" at the shell prompt.)
#
# This file is automatically updated on xserver-xorg package upgrades *only*
# if it has not been modified since the last upgrade of the xserver-xorg
# package.
#
# If you have edited this file but would like it to be automatically updated
# again, run the following command:
# sudo dpkg-reconfigure -phigh xserver-xorg
Section "InputDevice"
Identifier "Generic Keyboard"
Driver "kbd"
Option "XkbRules" "xorg"
Option "XkbModel" "abnt2"
Option "XkbLayout" "br"
EndSection
Section "InputDevice"
Identifier "Configured Mouse"
Driver "mouse"
Option "CorePointer"
Option "Emulate3Buttons" "true"
EndSection
Section "Device"
Identifier "Configured Video Device"
Driver "nvidia"
Option "NoLogo" "True"
EndSection
Section "Monitor"
Identifier "Configured Monitor"
EndSection
Section "Screen"
Identifier "Default Screen"
Monitor "Configured Monitor"
Device "Configured Video Device"
Defaultdepth 24
EndSection
Section "ServerLayout"
Identifier "Default Layout"
screen "Default Screen"
EndSection
Section "Module"
Load "glx"
EndSection
Espero ter ajudado.