No sound on laptop

Hello,

I have a sony viao laptop with Vista basic installed. I do not know what happpend but i cannot hear any sound wen i play anything. But wen i start my computer, the sound tht comes from windows wen it get started, i do get that but nif then i try to play any clip movie or anything, it didnt sounds. So kindly help me out. I kno this problems is kinda like not believin. I m also shocked but plz plz help me!!!