1998 Volkswagen Polo not startin

Basicly we fort that the battery had gone but after charging it we niticed whilst trying to start the car the live from the starter solinoid to the motor was glowing red hot so we cahnge the starter motor for a new one whilst doing this we cleaned uo the earth strap to the gear box now when we try to start the live wire going to the starter gets so hot that the rubber casing is melting in seconds it sounds loike the starter is jamed or the engine wont turn over but when turning the fly wheel with a screw driver it moves freely any help would be great help thank you