Hello,
You may want to keep this in mind from the owners manual.
DIGITAL AUDIO OUT (OPTICAL)
x When a digital audio system is connected to the DIGITAL AUDIO OUT (OPTICAL) jack, decrease the volume of both the TV and the system.
x 5.1 CH (channel) audio is available when the TV is connected to an external device supporting 5.1 CH.x When the receiver (home theatre) is set to on, you can hear sound output from the TV’s optical jack. When the TV is receiving a DTV signal, the TV will send 5.1 CH sound to the home theatre receiver. When the source is a digital component such as a DVD / Blu-ray player / cable box / STB (Set-Top-Box) satellite receiver and is connected to the TV via HDMI, only 2 CH audio will be heard from the home theatre receiver. If you want to hear 5.1 CH audio, connect the digital audio out jack from your DVD / Blu-ray player / cable box / STB satellite receiver directly to an amplifier or home theatre.
I would also try another device. Try plugging in a Blueray directly to the receiver through Optical Out and see if there is sound. That should narrow down the cause of your problem. GL!