how to insert data into a table

[eluser]Unknown[/eluser]
actually am done already this
but now no records were inserted in my table
why this happened?
i'l send the controler code
pls give me the suggestions
thanq

Code:

<?php

class Welcomenote extends Controller {

        
    
    function index()
    {

        $this->load->helper(array('form', 'url'));
        $this->load->library('form_validation');
        
        $this->form_validation->set_rules('firstname', 'Firstname', 'trim|required');
        $this->form_validation->set_rules('lastname', 'Lastname', 'trim|required');        
        $this->form_validation->set_rules('username', 'Username', 'trim|required|min_length[5]|max_length[12]|xss_clean');
        $this->form_validation->set_rules('password', 'Password', 'trim|required|matches[confirm_password]|md5');
        $this->form_validation->set_rules('confirm_password', 'Password Confirmation', 'trim|required');
        $this->form_validation->set_rules('email', 'Email', 'trim|required|valid_email');                
        $this->form_validation->set_rules('phonenumber', 'Phone Number', 'trim|required|numeric');                

        if ($this->form_validation->run() == FALSE)
        {
            $this->load->view('welcome_view');
        }
        else
        {
            $this->load->view('success_view');
        }
    }
    
    function form_insert()    
            {
            $this->db->insert('registrationform',$_POST);
            }    
}

?>