starter issues

Greetings! I am new here so hope I dont make too many mistakes. I am trying to help my father in law. He has a 1978 Monte Carlo Landau that has a serious starting problem. He turned the key and the starter ingaged... it has not stopped! Pulled the batterie cable and rehooked it up. starter still turning. Is this the ignition switch, the starter, or the starter solenoid? I dont want to start replacing everything. I am mechanicly inclined, just not real automotive inclined. Any help would be great! thanks.... Shawn