Unity not running scripts


I have never faced the problem before, restarted and created new several projects

The code is given below :

public GameObject box;
int i = 0;

void Start()
{
    Debug.Log(i);

    //Gen();   
}

public IEnumerator Gen()
{
    while(true)
    {
        GameObject tem = Instantiate(box, new Vector3( i , 0, 0), Quaternion.identity);
        i += 6;
        Debug.Log(i);
        yield return new WaitForSeconds(0.5f);
    }
    
}

// Update is called once per frame
void Update()
{
    
}

Try:

StartCoroutine (Gen());