Hi and thank for asking your question. Can you tell me how you have your DVD/VCR hooked to your TV?
Here is a picture of the back of your unit - are you using the left circled set or the right circled set of audio jacks?
Knowing that you had it working fine until recently makes a world of difference in your diagnosis.
You mentioned that while in the menu, the audio works fine - this is actually opposite of what is supposed to occur with this unit. It was designed so that while you are in the setup menu the audio is supposed to mute instead.
There are a couple of things you can try, but the unit may have to be serviced to fix your problem.
1) On the remote press the "audio" button (fifth row down, far right button). Press this button while playing back a few times to see if the audio starts to work normally.
2) Unplug the unit from the wall for at least one hour. This will reset all internal functions and possibly reset the audio problem as well.
Unfortunately at the user level, this is all that can be done to try to fix your unit at home. Further repair would need to be performed by a repair technician.