I am having a similar issue with a LG 47LA6200, The "PC audio input" jack's where I have my RCA's doesn't really work in the way the manufacture intended them to. They work more as an Ipod jack, They were specifically put on this TV for this issue yet they don't work. You may be having a similar issue. I have gotten them to play through my HDMI but it was through random plugging and unplugging and it switched my computer to 720p and when I either let the computer turn off or switched back to 1080p it would no longer work. If you don't mind play some audio (Music video from youtube works) and select another input that you don't have anything plugged into and see if audio comes through the empty port (Doesn't matter which on you select AV, Component HDMI) Then If I find a solution I can let you know and vise verse.