what do you mean blocked?
do you have a "volume control" icon on the task bar?

if not then go into the control panel > sounds and audio devices > on the volume tab there is a check box for volume control on the taskbar

(ironically this doesn't work for me, i get a message saying the necessary program is not installed and haven't been able to find the installer yet)

as for actual "permissions" i dont know of any that prevent audio use