Hi, what you need is a piece of software called a 'Driver'. These 'Drivers' are what enable things like your sound and graphics work. To get the correct driver you need to find out what type of sound 'Hardware' you possess. Did you get any documentation with the pc? You could also ask the store from where you purchased the pc. Once you have this information post back and I'll point you in the right direction.

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AMD X2 6400+ 3.2GHz BLACK EDITION::SCYTHE SAMURAI COOLER::GA-M51 M/B::3GB DDR2 6400RAM::GEFORCE 8800GTS320/625/900MHz DRIVER '174.74' BETA::160 RAID 0 SATA2::SOUND BLASTER AUDIGY/'DANIELS' DRIVERS::LITE-ON DVD RW/PIONEER DVD::HIPER 530W MODULAR::THERMALTAKE ARMOUR Jr CASE::RAZER COPPERHEAD MOUSE::VISTA HOME PREMIUM SP1