Audio not working when connected to HDTV

I connected my MacBook Pro to my Samsung HDTV LN40D503F6F and also connected an HDMI cable to the TV using Apple mini DVI cable. I tried connecting to both HDMI/DVI 1 and HDMI 2. Video works fine when connected to both the HDMI ports, but the audio didnt work. I also purchased an a 3.5 mm audio to RCA cable and tried switichin between both the HDMI ports but still it is not working. Any solution would be great. Thanks !!!