I have no audio in Penumbra: Overture

Make sure you have the latest drivers for you audio card.
Consult your computer or sound card manual to find out the manufacture of the sound card and where to download drivers. You can also use the DirectX Diagnostic Tool to find out what sound card you have.

See Related articles to find out how to use DirectX Diagnostic Tool to retrieve information on your audio card.
See Related articles on common audio hardware manufactures and their websites.

Get the latest OpenAL release
Penumbra: Overture comes bundled with an OpenAL installer. Chances are that a new version of Windows, your audio cards driver or a new audio card has created some problem. To make sure, visit the offical OpenAL site and download the latest release.

If neither of the above helped.
See Related articles to find out how to reset your audio card settings.
See Related articles to find out how to use the troubleshooting guide in windows to solve audio problems.
See Related articles to find out how to change the audio hardware acceleration level to solve audio problems.