if(isset($_POST['logIn'])){
    $checkLogIn = $this->config->logIn(); // sprawdzanie usera i nadawanie uprawnienien
    echo json_encode($checkLogIn); // wysylanie danych do jquery
}

$('#logInUser').click(function(){ //validation new report
        var infoAjax    = $('#infoAjax');
        var bgAjax      = $('#bgAjax');
        
        $.ajax({
            url:        'index.php',
            dataType:   'JSON',
            type:       'POST',
            data:       $('#form').serialize() + '&logIn=oo',
            beforeSend: function(){
                infoAjax.html('Trwa logowanie do systemu raportowania błędów<br /><img src="img/loading.gif">').css({'width':'400px',' position':'fixed','left':'50%'}).show();
                bgAjax.show();
            },
            success: function(obj){
                infoAjax.html(obj.info);
                if(obj.check == 1){
                    setTimeout(function() {
                        location.replace(obj.link); //load to new page after logIn
                    }, 2500);    
                }else{
                    setTimeout(function() {
                       infoAjax.fadeOut();
                       bgAjax.fadeOut();
                    }, 2500);
                }
            },        
            error : function(){              
                infoAjax.html('<p>Przepraszamy, ale logowanie jest chwilowo niedostępne.<br /><font color="red">Prosimy o kontakt z administratorem</font></p>');
                
                setTimeout(function() {
                   infoAjax.fadeOut();
                   bgAjax.fadeOut();
                }, 2500);
            }
        });  
        return false; // block load form action
    });

<div id="frameLogIn">    
        <img src="img/LogoSystemError.png" alt="System Raportowania Błędów" />                            
        <div id="logIn">
            <form id="form" action="index.php" method="post">
                <input id="inputLogin" type="text" name="login" placeholder="Login"  /><br />
                <input id="inputPassword" type="password" name="password" placeholder="Hasło"  /><br />        
                <input class="submit" id="logInUser" type="submit" value="Zaloguj" />
            </form>
        </div>
    </div>
    <div id="infoAjax"></div>
    <div id="bgAjax"></div>