MN31/N no sound

I can't get the sound to work on my mother's MN31/N. According to
device manager everything seems ok. In the Sounds part of Control
Panel I can click the button to play a sound but nothing comes out.
All the nVidea panels look right.

The AC97 is set to Auto in the bios.

I have the speakers (just two) plugged into the jack closest to the
monitor connector, which should be the right one although I've tried
the other two also.

Any suggestions? I'm getting ready to put in a sound card I have lying
around because she's heading off to Florida in a few days, as soon as
the power is back on down there, and she needs the sound working.