got any ideas on this?

[eluser]mistress_shiira[/eluser]
good day guys!im still new to CI and ive been trying to learn how to use a framework such as this.
im currently redoing an admin page that i have developed without using any framework before.i would like to redo it using CI.unfortunately, i have come across this problem.hope you can tell me how to go about with this.
actually i have this code:

function index(){
$this->load->library('validation','session');
$this->load->helper('form');
//set validation rules
$rules['username'] = "trim|required|callback_check_input";
$rules['password'] = "trim|required";
$this->validation->set_rules($rules);

//set validation fields
$fields['username'] = "username";
$fields['password'] = "password";
$this->validation->set_fields($fields);

if ($this->validation->run()) {
$query = $this->db->getwhere('users', array('username' => $this->input->post('username')));
$row = $query->row();
$this->load->view('cpats_main');

}
else{

$this->load->view('cpats_admin');
}
}

actually it already works,i can log in and proceed to the next page.the problem is that when i re enter the URL and hit enter,the page goes back to the admin page.how can i avoid it doing that?