Download the latest Drivers.
Of course you may be in the position that I am. My MOBO/Chip are so old the there are not Drivers available for W7! (Vista are the most up-to-date
So I bought a USB Sound Dongle, for less than a £5'er including postage. Of course it's not as good as my HiFi, but neither was the PC before, when it ran WXP.