First, pull the chain to release the articulating bracket from the e-center so you can pull the TV out to look at the connections behind it. There should be an audio cable with red and white RCA plugs connected to the audio out jacks on the back of the TV. The other end of the cable should go to one of the audio inputs on the back of the receiver. There should also be another cable with 3 RCA jacks (yellow-red-white) that deliver video and audio to the TV so you can watch DVDs.
Once you have confirmed the cables are in place and connected properly, the receiver volume is dependent on the TV volume. You may have to "pre set" the receiver volume higher than you would normally have it, and then adjust the volume level with the TV remote. Be aware that if you switch from the input for TV sound to another setting (like the radio) before turning the receiver volume down, you and everyone else may jump out of their skin. You can guess why I know that.