This may be really stupid, but it is often the simplest things that get overlooked ! You haven't got the 'Mute' switch on have you ?
I think there is a physical switch for this on the Vaio, above and to the right of the keyboard. Failing that, there is normally a little loudspeaker symbol at the right hand end of the task bar which, if you click on it, will show you the state of the mute switch and volume level. And if that doesn't work, 'Control Panel' - 'Sound'.
Best of luck,