have you tried moving the "xorg.conf" to "xorg.conf.off" (keep a backup, but try booting without it).
xorg will attempt to identify your hardware on the fly.
you can also jump to console, stop X, then run another xorg configure;
from the man page:
-configure When this option is specified, the Xorg server loads all video driver modules, probes for available hardware, and writes out an initial xorg.conf(5) file based on what was detected. This option currently has some problems on some platforms, but in most cases it is a good way to bootstrap the configuration process. This option is only available when the server is run as root (i.e, with real-uid 0).
will attempt to create a vaild base for an xorg.conf