[Richard Crowley]

wrote ...
This is unbelievable. At the risk of looking like a total moron, I
thought I'd share with you how I managed to fix the problem. I went to
my father's to see why his SoundBlaster card is working and mine
isn't. It turned out to be something really minor. His speakers were
plugged into the green jack (A), I was plugging mine into the blue one
(B) SEE PICTU
http://i70.photobucket.com/albums/i9...g?t=1231445495
It never occurred to me to use the green jack because since building
this computer in January 2008, I have ALWAYS used the blue one for my
speakers! I have no idea what the hell happened, I'm just glad to
finally have sound again.

Some of the consumer sound cards have dynamic "auto-sense" where
you can plug into almost ANY jack and it will either figure out what
you want, or it will pop up a window and ask you.

I find those kinds of automatic things (like "plug-n-pray") to be very
annoying. I have a sound card in a system here in the office that is
always going mute, and then I have to take the box out and unplug
and then re-plug the connector to get the pop-up window to show
so I can tell it AGAIN that I yes, I want the conventional line output
on the green jack. There is apparently no way of turning OFF this
stupid "automatic" behavior.

And you have discovered annother downside to this automatic behavior:
It trains the user to think that it doesn't matter where you plug something.