Well, there is always the chance that your system does not play nicely with 'Xorg'. What hardware are you running on?
For a lot of users the "confless" mode of 'Xorg' seems to work quite well, that is to not supply a specific config file. If I were you I'd try first Xorg -probeonly and analyze the error / warning messages. You should also take a very good look at '/var/log/Xorg.0.log'.
With sudo Xorg -configure you could "ask" 'Xorg' to create a skeleton config file. You could then apply your changes to this file and either copy it as 'xorg.conf' to '/etc/X11' or use Xorg -config /path/to/the/new/xorg.conf.
There is a lot of material to be found on the net about all this. I agree it can be at times confusing, so please take care when reading to check that the information is current. Quite a few things have changed over the last few years so things that were correct 3 years ago might not be so any more.