Maybe its your mobo driver only support up to XP only, happened to me also din notice that my mobo driver din support Vista , dled vista version from the net and it solved the problem + sound back.

To those who want to upgrade XP to Vista, this is a good guide and for you to decide whether to upgrade or not, i read this b4 i upgrade too. though i see your specs........i think gonna take a loongg way to upgrade

Link Here