VoiceAttack itself runs in a single, foreground process.
Have you tried restarting your computer? Is the microphone you are trying to use the Windows default recording device?
If the recording device is not available at all times (E.G. you need to don the headset in order for it to become available), you may need to either restart VoiceAttack entirely, or use the "Reset Speech Recognition" option in the title bar context menu (click the VoiceAttack icon at the top left-hand corner of the main window) to register a change in the Windows default recording device.