HDMI Input Problem, No sound. HELP!!

Hi everyone, Im not sure if this is where I should post the topic, but Im having problems with my HDMI Input on my Alienware M17x R3.

Basically the picture quality is great and it works well, Except there is no sound coming out. (if connected to a xbox, ps3, dvd player etc)

Does the HDMI input have sound in built into it? 

Any help guys would be awesome

Thanks :)