Have you tried the update driver option?
As you have reformatted your computer you will probably need to reinstall the drivers. If windows won't update when you tell it to, you'll have to go to the manufacturers site - if you have a PCI soundcard added then go to their website. If it's onboard sound, try reinstalling the motherboard drivers. You maybe still have the disk with them on it that came with the computer/motherboard, if not they should be available at their site.
To find out your motherboard model etc you can download this free program ...EVEREST Home Edition
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