Perhaps the ati.lzm will help us, before I try everything on an external monitor.
then run startx
still not solved the problem?
there should be more then 1 xorg.conf file like xorg.conf.orig or xorg.conf.backup or xorg.conf.old
then copy the backup file over orignal xorg.conf
still not solved final solution
this will solve your problem.it would replace the xorg.conf file with the original/fixed one.