Tutto qui?
Pensavo Ubuntu configurasse più roba
Mancano tutta la parte del mouse e della tastiera... Sei sicuro di avere copiaincollato tutto?

Comunque io proverei a modificare così:

Spoiler:

# 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.
#
# Note that some configuration settings that could be done previously
# in this file, now are automatically configured by the server and settings
# here are ignored.
#
# 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 "Monitor"
Identifier "Configured Monitor"
EndSection

Section "Screen"
Identifier "Default Screen"
Monitor "Configured Monitor"
Device "Configured Video Device"
DefaultDepth 24
SubSection "Display"
Depth 24
Virtual 1680 1050
Modes "1680x1050@60"
EndSubSection
EndSection

Section "Module"
Load "glx"
EndSection

Section "Device"
Identifier "Configured Video Device"
Driver "nvidia"
Option "NoLogo" "True"
EndSection


Così dovrebbe fissare la risoluzione corretta.

In ogni caso se non dovesse più avviarsi l'ambiente grafico, loggati nella console con il tuo username e password poi dai

Codice:
sudo dpkg-reconfigure -phigh xserver-xorg
Che ti farà ritornare il tutto come era prima