Windows XP machine is not making 'event' sounds

Windows XP machine is not making 'event' sounds

My neighbour has a machine running XP that no longer makes Windows 'event' sounds, such as the Startup/Shutdown sounds. I've checked all the obvious things. If I go in to edit the sound scheme, I can see the sounds are assigned to the event, I can click the little 'play' button and it plays the right sound. It just won't make any noise on its own.