Well the main thing it would suggest is that either the mechanism is being jammed by the cassette or that the take up spindle is not turning through some defect in its drive. If you aren't a technically inclined person there is nothing you can do, as the case would require partial dismantling to check the mechanism. This said assuming that you have tried more than one cassette and that the battery is fully charged, or that you have the mains power supply connected whilst testing.