Woke up one morning and no sound.

I've checked all the physical connections, verified that the sound is
down across all applications,and checked that the speakers work with
other things. Our computer is connected to our stereo.

The sound test shows it is playing a sound, but I cannot hear it. I
get an error message if I choose OSS to run the test with (not found
or busy),but everything else lets me test the sound OK... I just
cannot hear anything!

I would like test to make sure my sound card is OK, but don't know how
to do that?

Does anyone have any other suggestions?