Windows sometimes fails to detect the default playback device automatically.. Try doing it manually.. Right click on the volume icon on the task bar and select playback.. Click on speakers and select properties.. If your device is shown listed in the drop down menu then select it and click apply.. Do the same for microphone..
Alternatively, run dxdiag and click on the sounds tab.. Check if your device is listed.. Run windows update and click on search for updates.. Windows will gather information available on any updates which are available for any of your devices or software.. It'll list drivers regarding your sound card too (if required and/or available)..