https://bugs.freedesktop.org/show_bug.cgi?id=64850
--- Comment #15 from Jakob Nixdorf flocke@shadowice.org --- Nothing of the things you suggested worked.
Without xorg.conf the problem is still present.
Booting with only DVI-0 plugged in works fine. If I plug in HDMI-0 with X11 running everything stays the same and the HDMI monitor says "No signal", when I try to activate it via xrandr both monitors switch to black. If I plug in HDMI-0 in TTY the TTY is switched to the HDMI monitor and the DVI monitor goes black.