go to /tmp and see if there are any files there
if so, erase them all (must su and don't start anything)
you can find the log in /var/log/XFree86.0.log or it could be something like XFree86.8.log but that is too rare. there is the log file . post it here (at least the lines with WW and EE) and we'll look into it
meanwhile you could try dpkg-reconfigure xserver-xfree86 and it just might do the trick
