Please share the status of 'audio devices' in the 'Device Manager'. A screen shot of that page would be most useful.
To access 'Device Manager' page, follow the steps listed below:
Click 'Start' > In 'Search programs and files' text-box type 'devmgmt.msc' (without quotations) > Tap 'Enter'
Also share the name/details of 'sound card' that you installed; would like to know about the drivers that you installed. (Did you install the drivers using an installation disk or a link on the internet)
Do reply with the details; would be glad to assist.