The last line in your xorg log is caused by switching to another terminal.
After getting the black screen, try switching to and from a terminal (e.g. Ctrl+Alt+F1).
Thanks for the post, but I did that myself top copy the log file of that session to my home direcory (and edit xorg.conf to use the OSS driver to get again something on my screen and post on the forum).
Well, why don't you back up your current xorg.conf somewhere and start a new one with "sudo dpkg-reconfigure xserver-xorg". When you finish that, either edit the new xorg.conf to use fglrx or "sudo aticonfig --initial". See how that works.
(Oh, and post the whole log at some pastebin service so I/we can take a look at it.)
By the way, when you say "OSS driver", you mean the ati/radeon driver, correct?