unable to hear sound

helllo everybody i installed ubuntu 8.04 within windows with a choice during boot successfully and inow i am unable to connect to internet but when i tried to play mp3 files using totem player ,first it download some files and installed them after that it shows playing my file ut there was no sound i also check system sound it was on full level,same is the case with totem movie player and i am using a laptop and my speakers works fine in windows, please help me i am using linux or ubuntu first time