When all else fails, yank the drivers and reinstall.
Before doing that though, pop into the control panel and check out "Sounds". Highlight any one of the sounds that are set, and see if the play button stays greyed out or turns black ("usable"). If it goes black but nothing plays, you've probably got a dead card. In either case though, boot to safe mode and open device manager. Yank anything that even looks like a sound card under "sound, video & game controllers" and reboot. Have your driver disk handy in case Windows doesn't have the .inf, but it should.
One other thought - if it's that old, might it be an ISA card? If so, before yanking drivers double-click "computer" at the top of the device manager list and see that nothing is trying to share an IRQ with it. Generally, ISA cards hate that.