If you have INTEGRATED HDMI Audio like the ATI 740 or 780 chipzet, and installed all drivers you will have a "ATI SOUND OUT" or somethign similar as audio device, this device is used to output audio to the HDMI, the problme is that sometimes windows doesnt know whichw ay to send you audio trough the "HD Raltek Audio output" or the "Ati audio output", so to make usre go to control panel and into sound options, to the third tab i think its sound device, and use the Realtek HD one, or whatever sound card you use, it is probably set to the HDMI output
ventrilo knows that you want to use the normal outputs and sets it
that happened ot me, if this isnt it, sorry ;S