http://www.toshibadirect.com/td/b2c/cfam.to?coid=-26377
Wich one ? There isn't any A-906
LE: found some satellite A100-906 seems to be manufactured for Russia. Or at least is debated on russian sites.
LE2: Be sure you have the sliders for sound to a level different from zero. And also try to swich in audio preferences the output device from default to direct sound or Realtek AC97 or something else (not modem if present)