Ford fiesta and it won't start i got a new starter motor but it still won't start what could it be?

Could be heater plugs if its a diesel or maybe the battery.

Check the earth (ground) cables between the engine and body for cleanliness and security of connection. Turn the ignition key, you should hear the starter solenoid 'click'. If it does, the cable from the battery to the starter is a fused link, connect a starter cable between the battery and starter motor solenoid and try to start. If there is no 'click' the fault is either the ignition switch or the wiring from the solenoid to it. If the car is automatic it should only start in Park (P) and Neutral (N). check the operation of the gearbox start inhibit switch. If an aftermarket alarm is fitted check the security and cleanliness of the wiring connections, especially the immobilizer circuit.