|Also check to make sure that the sound is enabled on the actual device:|
- Go to Control Panel
- Go to Sound/Audio Devices
- Select Hardware then the drive in question
- Go to the Properties tab
"Enable audio for this CD-ROM device" should be selected. If it's not, that would explain the lack of audio on DVDs and CDs.
I assume you're not having any trouble with videos on Youtube or sound that isn't linked to the DVD drive?