First look in Device Manager to see if you find any yellow or red warning/error signs -
Then in "Sound and audio properties" click on the Volume tab then the "advance" button in "sound vol"
Make sure a panel titled "wave" is shown and the volume is turned up and that the Mute is not ticked.
Now click on the Sounds tab - at the bottom for each Program event eg "Asterisk" - highlight the item and in the "sound" box a corresponding wave file (*.wav) should appear - to the right of this (and to the left of the "browse" button) you will see a triangle on its side - click on this and you should hear a sound. If not let me know.

Peter