A common problem that is easily fixed by making sure that your recording source is activated and not muted. This is usually why you can hear the sound through the speakers but it only records silence to the hard drive.

XP Checklist for Windows XP users:

• Double click your speaker icon* in your system tray to bring up your mixer.
  
• Select "Options" and "Properties".
  
• You will see a radio button with Playback selected. Move this to select Recording.
  
• In the area below make sure that "Line In" is ticked.
  
• When you click OK the mixer will have changed to the Recording Control window.
  
• Make sure that the slider control for Line In is moved to the top.

* If you don't have a speaker icon in your system tray you can access these settings by going to Control Panel / Sounds and Audio Devices and clicking the Advanced button on the Volume page.

Vista Checklist for Windows Vista users:

• Right click your speaker icon* in your system tray and select "Recording Devices".
  
• Double click "Line In".
  
• Make sure that "Device usage" is set to "Use this device (enable)".

* If you don't have a speaker icon in your system tray you can access these settings by going to Control Panel / Sound / Recording.