Swtor uses your Default Sound Settings; without the game running you must go to your Windows Desktop, in the bottom right corner down by your clock you will find a white speaker icon, right click this and select - "Playback Devices".... Now select the device you wish to use and ensure that it is set to the Default, it should have a green icon over the device.
Now try your game again.
*Sometimes a windows update or plugging in a headset can change this setting, its nothing major just follow these steps when it does happen.
