What type of soundcard, or on-board sound, are you using? If you're using a soundcard, is it properly seated in the PCI slot? Are your speakers properly configured (plugged in, set up properly in your software)?
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AMD X2 4400+ Toledo 1MB/Asus A8N-SLI Deluxe/2GB Kingston HyperX/SLI Gigabyte 7800 GTX 256MB/Creative SB Audigy 2 ZS Plat w/ Creative Inspire 6.1 speakers /180GB Hitachi PATA/19\" AG Neovo F-419 LCD/OCZ PowerStream 600W PSU/WinXP Home SP2