i have a dell studio 15 and i am trying to connect to a sony bravia hdmi?

[Hina]

i have a dell studio 15 and i am trying to connect to a sony bravia 1080p tv with hdmi cables, the picture works great but i get no sound. i have windows 7. PLEASE HELP ME!!!! when i go to playback in the sound menu all i see is speakers/headphones and idependent rtc headphones as options