The following problems apply to some ATI graphic cards with an HDMI ouput connector.

No Sound
Append "blacklist snd_hda_codec_atihdmi" to /etc/modprobe.d/blacklist , reboot

Black screen

If your system is booted with a cable plugged into the HDMI output device you may just get a black screen on your main LCD, to fix this:

Unplug the HDMI cable and boot, once the graphical system starts up, plug the HDMI cable.

Open a terminal and type: xrandr, you will get a list of the detected displays, check the list of your HDMI capable device (on my case DVI-I_1l)

 Now let's edit the gdm init file, execute the command: gksudo gedit  /etc/gdm/Init/Default, go to the bottom of the file, and before the "exit 0" add the a line with:

xrandr --output DVI-I_1 --auto

You should now be able to boot with the cable plugged without problems.