Comment # 13 on bug 82473 from dimangi42@gmail.com

(In reply to comment #10)
> Just to be clear is it a problem specifically with HDMI or using any
> display?  Also make sure you fully uninstalled fglrx.  It overwrites some of
> the libs on your system with it's own versions.  You can also try disabling
> acceleration.  Add:
> Option "NoAccel" "true"
> to the device section of your xorg.conf

Disabling acceleration boots fine, and I get graphics as expected.