To find the listing click on the Darnya button, in the middle column at the bottom you'll see a preferences button, click on that and then in the right hand column, scroll down to "screen resolution"
Are you running at the proper resolution with crappy refresh? If so you'll need to find the Horizontal and Vertical refresh rates for YOUR SPECIFIC MONITOR. You should be able to Google them up, if you don't know your model # it's usually on a sticker on the back of your monitor. Once you have them you'll need to edit those values into your xorg.conf file. It's easy
Just open a terminal window and issue the following.
1: sudo cp /etc/X11/xorg.conf /etc/X11/xorg.bak (this makes a copy of your original xorg.conf file you can switch back to if disaster strikes)
2: sudo gedit /etc/X11/xorg.conf (this will open your main video config file in a handy dandy text editor)
scroll down to the section of the file that looks like this:
Identifier "Generic Monitor"
HorizSync 30.0 - 70.0
VertRefresh 50.0 - 160.0
replace the values you see there with the one's you've found for your specific hardware, MAKE NO OTHER CHANGES UNLESS YOU KNOW WHAT YOU"RE DOING
Save the file and close the editor. Now restart your 'puter and you should be good to go.
in case it won't boot to GDM and gives you a black text screen, login as prompted and type
sudo cp /etc/X11/xorg.bak /etc/X11/xorg.conf (this places the old conf file back in place and should get you back to square one if needed) reboot and you're back.