First make sure you have the correct drivers. http://support.creative.com/Products...=Sound+Blaster
Then go to the creative console in your start menu so it looks similar to this.
Now go here in your windows control panel that looks similar to this and double click the speaker icon. I think the icon in your system tray might work also.
Check the playback and recording playback as bruce explains.
Disable the line-in of the Playback
The line-in of the Record
Mixer is enabled. PLAYBACK MIXER Attachment 10489 RECORD MIXER Attachment 10490
See that REW settings look similar to this except with the soundcard calc loaded and then adjust as needed.