This is probably an issue with the Sound drivers or a bad configuration for the sound setting.
Firstly, go to Device Manager (Windows + R > devmgmt.msc) and make sure that all the devices are installed properly. This means no yellow or red items listed in the tree.
If there is something yellow, then most likely it's the sound device and you'll have to install the device driver to restore its functionality.
Secondly, open PowerDVD and go to the Settings menu. In the Audio section, change the device to reflect the one installed on your system.