my sound doesnt work on ubuntu 9.10

my sound doesnt work on ubuntu 9.10

i have a hp pavilion s7320n Slimeline pc with onboard audio. how do i get audio to work? i went to youtube to do a test run on audio. i installed the flash player and the video plays but no audio. i also tried to download a mp3 file to test the audio and nothing. what can i do?