Have you checked to make sure that sound is enabled for it in your sound control panel? There is an option to mute it, make sure it does not have a check mark under the cd audio slider.
If you have a little speaker icon in the lower right side of your screen, right click on it and open the volume control. If you see the cd audio selection, make sure it does not have a check mark. If you do not see a cd audio selection open your sound control panel, at the top click on options / property's and select cd audio, it should then show up.