My guess is the audio volume is way down or the unit is not set for the function you want, that is on DVD when you want TV or the other way around. I can only speak about how we use ours, which is nearly everyday:
A. Use the remote rather than the control on the TV because it is more reliable. Sometimes the buttons on the top of the TV are not effective. Make sure there are fresh batteries in the remote. The remote should be pointed toward the bottom of the TV - that is where the receiver is.
B. For a using a DVD, do NOT try to insert a DVD until the unit is on and DVD is chosen on the menu. Unlike some units, putting a DVD in the slot does not turn on the unit and activate this feature. Also, the DVD goes in one way, label side to the wall, mirror side to you.
C. For audio, use the volume controls on the remote, and make sure the volume levels are up. The volume numbers are 0 to 100. The mid-range is good place to start.
D. For broadcast TV, nearly every time the tug is in a new place, the TV channels need to be re-programmed because digital TV signals are line of light - no broadcast tower, no reception. To scan for channels: MENU (button on the top of the TV), CHANNELS, AUTO SCAN
Hope this is helpful.