Spell Better uses Windows' Text-to-Speech feature, and needs the sound to be on. Make sure your speakers are switched on, and that volume is at a suitable level in the software controls in your system tray (bottom right of screen).
Can I change the voice?
Go to your computer's Control Panel, Text-to-Speech area. You can select any voice that is installed, and vary the speed of speech. Other voices are also available for you to purchase (www.cepstral.com has excellent voices). The demo uses a Cepstral voice, 'Callie'.