LG Home Theater System LHT754 no sound

This is a manual that should help you, it may even be your model but, it shows hook ups and has a page about the Simplink:
http://www.lg.com/us/support/product/support-product-profile.jsp?customerModelCode=37LH30&matchedModelCode=1000009240&searchEngineModelCode=37LH30&initialTab=documents&targetPage=support-product-profile#
Scroll down to manual, ckick on the one you want, and open. Typically, you would want to hook all video related units directly to TV, via HDMi, Component, RCA, etc., with the componenet video, you have to also have an audio cable, because the componenet does not carry sound. In other words, you want to hook things like, cable/sat box, DVR, etc., directly to TV then, use your digital optical out from tv to digital optical in on your home theater. You use your TV's menu to select what you are watching and you only have to use the one input setting on receiver to listen to all. If you try to route you units through the home theater system first, you may not get the best results and you may expierience lags between the video and audio.

You should have the HDMI plugged into the Home theater unit. The theater unit then is attached to the TV using the HDMI out.
The home theater unit passes the HDMI through to the TV while playing the audio for you.
You will likely need to select the correct source on your RT2910.
Here is a link to the manual.
http://www.1800customersupport.com/productdocuments/RT2910_RCA.pdf
See the section entitled "Connecting to HDMI Components" for an illustration of what I have described above.

LG documentation states:

When you use SIMPLINK function, you have to

connect to the OPTICAL IN 1 jack to enjoy TV
sound to your speaker system.

Basically you need to have the Audio go from TV to receiver and setup receiver to that Input to output surround sound to all speakers.

If you have a cable box or satellite receiver, hook that output into the receivers input and that should work.

My setup is DirectTv HDMI output goes into the LG Home Theater HDMI Input 1, and LG goes HDMI output into the TV HDMI input 1.
so to watch DirectTV, I switch LG Home theater to HDMI Input 1. and TV is on HDMI input 1 (to view LG HDMI output from DriectTV, Blu-Ray, Vudu, etc.)

no just use the hdmi out on your tv

the HDMI cable sends dato TO the TV, it does not have enuf bandwidth to send both to and from, just TO. 

(got the video to play through the speakers and not the audio) how do you see video in your speakers?

Hook a digital optic cable from the Tv's digital ouput to the Recievers digital sound in. This should fix it. You might have to switch the input of the reciever.

no sound out of my Lg-lht754 system, only video. Could someone help me out.

Run a regular RCA type audio cable from your TV audio out to your Home Theatre audio in. That is what I have done recently with my Samsung LCD and Home Theater. You then have to put your Home Theater on Aux 1 or Aux 2 to get the sound from TV. Ensure your TV's volume is off.
Kurtis