No audio out to HDTV

Prior to building my own rig I had a Dell Inspiron desktop which was connected to a 47" Vizio LCD TV. I was using the integrated speakers in the TV by sending audio out the speaker channel (the green jack) and into the TV's stereo component audio input using the appropriate 3.5 mm to RCA cable. It worked great.

Now, I've built a new rig and the I have the audio set up the same way but with one setback... It doesn't work. When I plug external speakers or headphones into the jack it works great but the audio to the TV just won't.

Does anybody know whats the problem here? Or any other ways of getting sound to the TV. I have no HDMI so thats not an option unfortunately.

Thanks in advance!