First of all what os are you using? If its win xp make sure that you have both the microsoft UAA HDMI audio class driver and the ati hdmi auido drivers installed. Also not all DVI to HDMI cables are capable of carrying the audio signal, the cable that I own will not pass audio through. That could be an issue. Win 7 all you need to install is the ati hdmi audio driver which is included in the cat driver installer package.. For win xp, it is a seperate download from the main cat driver install package. As for for Vista i'm not sure, as i completly skipped vista.