A yellow ? in device manager means Windows doesn't know what the actual device is, which in turn means the device driver is not installed. If you fitted the sound card yourself, you should have it's driver on a separate CD somewhere. Otherwise you need to identify it's make/model and get the appropriate driver from their website. To help you identify it, install 'Everest Home Edition' and it will list all devices on your system:
http://www.lavalys.com/products/over...?pid=1&lang=en