Salve!
Seja bem vindo !
Já tentou escolher na tela inicial(Grub) ,o modo de recuperação ?
Boa sorte!
Ola também acho que o karmic está com muitos erros.
esse é o xong que funcionou comigo no koala, fiz manualmente, para um monitor de 14'.
# xorg.conf (X.Org X Window System server configuration file)
#
# This file was generated by failsafeDexconf, using
# values from the debconf database and some overrides to use vesa mode.
#
# You should use dexconf or another such tool for creating a "real" xorg.conf
# For example:
# sudo dpkg-reconfigure -phigh xserver-xorg
Section "InputDevice"
Identifier "Generic Keyboard"
Driver "kbd"
Option "XkbRules" "xorg"
Option "XkbModel" "abnt2"
Option "XkbLayout" "br"
Option "XkbOptions" "lv3:ralt_switch"
EndSection
#Section "InputDevice"
# Identifier "Configured Mouse"
# Driver "mouse"
# Option "Device" "/dev/ttyS0"
# Option "Protocol" "microsoft"
#EndSection
Section "Device"
Identifier "Configured Video Device"
Boardname "NVIDIA GeForce"
Busid "PCI:0:13:0"
Driver "nvidia"
Screen 0
Vendorname "NVIDIA"
Option "NoLogo" "True"
EndSection
Section "Monitor"
Identifier "Configured Monitor"
Vendorname "Proview"
Modelname "Proview PBROlc8"
Horizsync 28.0-96.0
Vertrefresh 49.0-85.0
modeline "800x600@85" 56.3 800 832 896 1048 600 601 604 631 +hsync +vsync
Gamma 1.0
EndSection
Section "Screen"
Identifier "Default Screen"
Device "Configured Video Device"
Monitor "Configured Monitor"
Defaultdepth 24
SubSection "Display"
Depth 8
Virtual 800 600
Modes "800x600@85" "1024x768@60" "640x480@60"
EndSubSection
SubSection "Display"
Depth 16
Virtual 800 600
Modes "800x600@85" "1024x768@60"
EndSubSection
SubSection "Display"
Depth 24
Virtual 800 600
Modes "800x600@85"
EndSubSection
EndSection
Section "ServerLayout"
Identifier "Default Layout"
screen 0 "Default Screen" 0 0
EndSection
Section "Module"
Load "glx"
Load "v4l"
EndSection
Section "ServerFlags"
EndSection