"the signal is out of band" on a black background.
Your video card is sending either a horizontal or vertical signal to your monitor that is beyond the ability of the monitor to sync on. This has happened because of the change you made to the /etc/X11/xorg.conf file.
First some advise, any time you decide to fix, adjust or other wise mess with this file back it up, before you muck around. Then if you get it wrong, you can just copy the backup file over the screwed up file, and you are back where you started from.
How did you change the configuration? Was it through MCC?
Did you use the on screen test first? Did it work?
There are several ways to fix this up. One is to boot the live CD and look at the /etc/X11/xorg.conf file and write down the horazontal and vertical frequencies that work, and the resolution. Then mount the disk and edit the file on the hard drive to match what works. When you boot the live CD, the files are all in memory.
That will get the system back to where you started. Now you have it working again, back the file up. Use MCC to do any adjusting of resolution, and test it, before you save the file and re-boot. If it works, I don't think the re-boot is necessary. It should allow you to change resolution on the fly.