If Windows system sounds play but audio CDs do not, take a look
here.
Test your speakers by plugging them into the headphone jack on your CD-ROM drive and playing a music CD. This bypasses the sound card.
Open the Multimedia utility in Control Panel (Start>Settings>Control Panel) and select the Audio tab. Make sure that your soundcard’s Playback device is selected in the Playback section.
Open the System utility in Control Panel and select the Device Manager tab. In Device Manager, open the Sound video and game controllers branch. Click on the name of your sound card to select it, then click on the Properties button. In the Sound Card Properties dialog box, select the General tab and verify that Disable in this hardware profile is not checked.
On the Start menu, point to Programs, Accessories, Entertainment, and then click Volume Control. In the Play Control window, click the Advanced button below the Play Control Volume slider. In the Advanced Options for Play Control window, if there is a check mark in front of Digital Output Only, then digital output is enabled. (Note: If there is no Advanced button underneath the Play Control Volume slider, click Options, and then click Advanced Controls.) If it's not checked, check it. If it's checked, uncheck it. If that doesn't fix things, go back and set it the way it was originally and try some sound again. Sometimes toggling things will set it right.