If you see a "b" on your screen, it is an indication of a battery issue. (Other indicators are a clicking sound or resetting of the lessons to Lesson 1.)
First, remove the batteries for at least an hour and insert a new set of high-quality, brand name batteries such as Duracell or Energize, not store-brand. Also, do not use rechargeable batteries, as the internal components are not compatible.
If these suggestions do not work, please contact us at firstname.lastname@example.org letting us know when and where you purchased your system.