Trying to Get Sound From My Sony Vaio to my TV

I have a Sony Vaio NW series laptop and a Samsung HDTV. I'm connecting my laptop to my TV using an HDMI cable and plugging it into the DVI port. Video works perfect but sound doesn't work because my computer's sound card doesn't support HDMI. Now I'm using an RCA 3.5 male cable using the headphone jack but I still can't get sound from my laptop to my TV. Am I doing something wrong? Please help. Thanks!
 
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