Vista - s/pdif output does not work on receiver

Hi, I am new to this forum and do not know to much about computers, so after hours of searching for a solution I decided I would try asking someone with a lot more knowledge then me. I have a Gateway with Vista Home Premium 32 bit operating system with SigmaTel high definition Audio CODEC driver with the latest upgrade. I am trying to use my s/pdif output on my computer to have audio over my home surround sound speakers via my home receiver. But when I plug it in and switch my receiver to the appropriate place I get nothing out of the speakers. From the cord I am getting the red light so I know it is getting the "power" but I am just not getting any sound. In the control panel under sound all the appropriate boxes and devices are enabled and say they are working, but I still can't get it to work. Does anyone know why this is? Is this a software/driver problem or do I need to "flip a switch" in some window I don't know about or what? My two front speakers with the single green plug work, but having them plugged in or not does not effect whether my receiver has sound or not. I have tried several different plug-ins on my receiver and none of them will pick it up, but they work with other devices, i.e. dvd player, and cable box. So I have eliminated a problem with the receiver. Any help with this would be much appreciated thank you in advance.

You have to switch to “digital output” from the sound applet and then – "set as default". Vista works simultaneously with the sound devices.
To have DTS or DD you have to use ffdshow or vista codec pack.

Thanks for your help but I already got it resolved, I didn't change the output on my receiver to optical and it was on coax. Thanks anyways