I'm connecting my PC to HDTV (Plasma) in livingroom but I have video ,but no audio. I'm using VGA w/3.5mmaudio plug running to converter box switching to HDMI. Both ends of VGA cable have 3.5mm plugs. The end going into the converter box (audio)plugs into box. Don't seem to have a place to plug audio plug at computer. Could this be plugged into S/PDIF jack. Don't really know the purpose of S/PDIF. Help me out, Please & THANX