Can you please check the output device in the Options/Plug-ins page. The selected device should be "Default DirectSound device" or any other device name starting with "DirectSound:". If nothing is select, it's also ok, it's the same as "Default DirectSound device".
That's strange. Did you try this with different file type, such as WAV, WMA and MP3? Do you have a chance to try Raduga on a different computer? Maybe it's a problem with the sound card.