Some more details would be a great help in solving this one... No sound at all? check to see if the speakers are muted. If that's not the problem, then try turning the volume up if you have a volume control on your keyboard... Other than that, can you be more specific?
I would try rolling back the driver, and if that doesn't work, go to the manufacturer of the computer's website(or the sound card) and re download the vista drivers from there. Then install them from the control panel --> sound applet.