Method depends on your OS and model of motherboard. XP and W2K can probably both find the necessary files if Multimedia and graphics are integrated. If not, you will need the manufacturer's drivers.
First look in C Panel > System > Devices > Hardware and see if Multimedia and Display hve little yellow triangles with black exclamation marks by them? If they have, right click & delete the drivers. Reboot and next time Windows boots you may have everything working again.
If not, tell us a bit more about your OS and motherboard
Quick question, Was the Programs on the Computer when you got it? if so and you got a Recovery disc. Save all your Docs and Photos etc to CD or DVD then restore with Recovery disc. This will mean that you will have to reload any XP updates but it should also get your sound back
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