Posted 01 July 2009 - 05:53 AM
Check your Realtek software (should be a blue icon like a crab in your taskbar by the clock, or even a red speaker icon in some cases) sometimes the default jack assignment settings are incorrect or re-assigned (i dont have a realtek here at work so unfortunatley cannot walk you through the settings). Also the ATI HD3400 most likely has an onboard sound card if its a HDMI version, that could have interfered with your setup. Open your control panel/Sounds and Audio Devices, click the Audio tab at the top and ensure the correct device that you are pluging your TV into is the Default Device in the Sound Playback section at the top.
Hope this helps