Well back up your current XF85COnfig file first. This can be done like this
mv XF86Config XF86Config.NONWORKING
That should back up the file (by renaming it). Then you can restore one of your older files like this
mv XF86Config.old XF86Config
The next thing to do would be to try getting the X Server back up again. First, switch to run level 3 to make surte the X server is completely off
su -c 'init 3'
password: <type root password here>
Then you can switch to run level 5, which should automatically attempt to start your X server for you
su -c 'init 5'
password: <enter your root password here>