computer speakers

I just bought a new monitor for a Sony RZ20C, and it's working fine.
But I've tried hooking up the speakers that came with the computer for the
first time and am having no luck getting them to work (I was using an old
CRT monitor with built-in speakers). The
speakers are fresh out of the box and I'm sure I've got them connected
properly. I don't think they're broken, since they do make sound when the
power is turned on. Is this a driver issue? I tried reinstalling a driver
from the application recovery CD, but get the message that there are no
updated drivers.

If it helps, I know it's not a volume/settings problem, as I can connect the
old monitor as is and get sound through its speakers.

If anyone has any ideas, I'd love to hear them. Thanks.