Did you check device manager? Is it listed there as OK? If not, install the driver for it from the PC vendor's support site, or the sound card vendor if it's an add-on card.
Similar situation with me as well. I checked device manager and it's listed OK there. Still then I am not able to play sound in my system. Some Sound mixer not available
this works on the devices on ur system go to the card to drivers the click update be online when u do this it will look on the computer first then go on the web for them when it starts the download click save then run, so will have them for later, it's always good to back-up all ur drivers & .dills on cd/rw 1 for each so next time on need 1 u pop in the cd & pow u got it.