So choose Recovery Mode, then login/exit to the command line, then:
mount -n -o remount,rw /
Above makes your hard drive read/write, which you'll need, in order to do the next step
sudo nano /etc/X11/xorg.conf
Use nano to edit your xorg.conf to fix it, ideally.
If you aren't in Recovery Mode, even if you can't see the screen, type in your username, then password, so, e.g.
alsdifuhsidu: [type username]
sldfhsd: [type password]
sldfhaksjhdf: <-- Your 'garbage' command line prompt.
You can reboot by doing: sudo reboot
sadklfjhsdk: [type password]
In any case, if you have rebooted using Recovery Mode, you shouldn't see the garbage output onscreen. Also, there is an option in Recovery mode to set 'Network' which changes your disk to read/write mode as well.