AddForce doesn't seem to affect the object it should.

I’m making a turret, which would shoot an object, selected randomly from an array, every couple of seconds. From several sources, and with several people’s help, I made this script:

public class shootingD : MonoBehaviour {

	public Rigidbody[] projectiles = new Rigidbody[5];
	public Transform MuzzlePoint;
	Rigidbody MyElement;
	public int magnitude;
	public float shootingWait = 2.0f;

void FixedUpdate()
			shootingWait = shootingWait+Time.deltaTime;
			if (shootingWait > 2.0f) 
				shootingWait = shootingWait - 2.0f;
				MyElement = projectiles [Random.Range (0, projectiles.Length)];
				MyElement.gameObject.SetActive (true);
				Instantiate (MyElement, MuzzlePoint.transform.position, MuzzlePoint.transform.rotation);
				MyElement.useGravity = false;
				MyElement.AddForce (Vector3.forward * magnitude*Time.deltaTime, ForceMode.Impulse);

The only problem is, that it spawns an object, which does not move. I’ve tried many alternate versions, and spent a day and a half working on this, but it still just spawns a static object.
Any help would be greatly appreciated.

You have to add force to the object you instantiated.
so it would be something like

GameObject Object;
GameObject prefab
Object = Instantiate(prefab,....)