Okay that is a tv issue then,
the setting you mentioned earlier for audio only is to shut off the tv screen and use just the speakers. That wouldn't apply here.
I do have a concern about the vga, because that is video only and would not be able to give you sound in the first place.
But if no sound from the cable box over hdmi either, that is a tv issue, either faulty amplifier or control board.
There is one step you can take here, both as a possible fix, as well as a diagnostic evaluation:
1) Unplug the power cord from the outlet
2) Wait at least 1 hour (60+ Minutes)
3) Press and hold the power button (on the set, not the remote) for 60 seconds
4) Keep holding power button while plugging back in, and for another 60 seconds after. When plugging back in, go directly to the wall outlet, bypassing any power strips or surge protectors.
Let me know the results.