Spravi si najprv zalohu konfiguraku x-ka.

sudo cp /etc/X11/xorg.conf /etc/X11/xorg.conf-backup

Potom zedituj konfigurak.

sudo gedit /etc/X11/xorg.conf

a tam by si mal mat nieco taketo:

Section "Monitor"
Identifier "External Monitor"
Option "DPMS"
HorizSync 62.0 - 72.0
VertRefresh 55.0 - 65.0
Modeline "1920x1080" 176.92 1920 2008 2224 2632 1080 1080 1083 1120 +hsync +vsync
EndSection
Section "Screen"
Identifier "External Screen"
Monitor "External Monitor"
DefaultDepth 24
Option "metamodes" "1920x1080 176.92 1920 2008 2224 2632 1080 1080 1083 1120"
SubSection "Display"
Depth 24
Modes "1920x1080_60.00"
EndSubSection
EndSection

Na kalkulaciu svojho monitora si pustit tuto kalkulacku:
http://xtiming.sourceforge.net/cgi-bin/xtiming.pl