I'm sure this question is an old one, but I am trying to find an answer so I am butting in here for help, please.
This is what is happening. I have had my Sony PRS505 for a few weeks and am listening to a book, and can't turn the audio off

If I turn the reader off, it's fine but as soon as I turn the reader on again and plug in my ear bud, I realize that the audio is still on. I've pressed every button to try and turn it off, and sometimes I'm successful with the big round button (the 'enter' button) and other times that doesn't work. Help me please. I'm sure it's something very basic and I'll probably want to kick myself when I get the answer.