[lug] Switching from daughter card to mother board resident sound "card"?

[siegfried]

Apparently when I bought my desktop computer from PC Club, they installed a
sound card as a daughter card that was redundant with a sound card on mother
board. As I (vaguely) recall, this was the solution to a knotty problem with
linux sound card drivers and Fedora Core 4. 

Last night I was listening to some MP3 files under windows and everything
was fine. This morning, it would not work and I had not rebooted since it
was working the previous night!

After failing to get any results, I replaced the "sound blaster" daughter
sound card with another new COBRA sound card (it was a couple years old,
however) and windows prompted me to install mfr's drivers but still no luck.

Then I noticed some little sound card plug/icons for the first time on the
back of the case! I had not noticed these before! When I decided to try
these out, they worked! 

So apparently, over night, some gremlins came to visit and flipped some
secret switch so I'm now using the motherboard resident sound "card". (This
is not really a card -- but what is it? Circuit?)

I have yet to reboot and try it with linux. I suspect it won't work with
Fedora core 4 because that was the reason for adding a daughter card in the
first place. Hmmm... another reason to update.

Where is this mystery switch that determines which sound card is is used:
the daughter card or the motherboard resident card? Why did the daughter
card suddenly stop working?

Thanks,
Siegfried