I cannot see an error in your Xorg.0.log except "error opening security policy file /usr/lib/xserver/SecurityPolicy", which is a remnant of http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=362246
seems similar to bug # 44370 , but that one has a fatal error. leaving as "needsinfo" [couldn't triage] -- Black screen with a ATI graphic card https://launchpad.net/bugs/62413 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
