Windows XP mixer settings
Before installing any of SDR software it is necessary to change some settings in Windows OS. First you need to set audio mixer output and input (recording) parameters. Fastest way to setup mixer properties is to double click at speaker symbol in system tray. Mixer window may look different according your sound card type. This is most common sound card mixer look.
After double click you will get mixer setting similar to this picture. Mute every signal source except Master Volume and Wave.