Congratulations on figuring it out on your own. That's almost always more satisfying than simply getting a quick answer, even if it's more frustrating at the time. You get to learn more that way too.
What you've discovered is that Linux systems always start out with the sound levels set to zero, something that does cause a lot of newbies to stumble. I don't know why
it's that way, but it is. Hopefully your post will help a few others out.
And here's hoping your next challenge is just as successful.