PHP session variable won't change - php

Question

UPDATE : I added all codes;
I want to create a login page for test purpose and I included attempt number with php sessions. The problem is session's variable isn't changing.
index.php
<?php
if (!isset($_SESSION)) {
session_start();
$_SESSION['attempt']=3;
}
if ($_SESSION['attempt']<0){
header('location:login_error.php');
}
require('../function/start.php');
$title = 'Login';
require('../template/header.php');
$ip = !empty($_SERVER['HTTP_CLIENT_IP']) ? $_SERVER['HTTP_X_FORWARDED_FOR'] : $_SERVER['REMOTE_ADDR'];
var_dump($_SESSION['attempt'])
?>
<h3 class="epad_header">Login</h3>
<div id="epad_wrapper">
<div id="ad_form_wrapper">
<form action="control.php" method="POST">
<fieldset>
<span class="formtext">ID</span>
<input type="text" name="epadName" id="epadName" required>
<span class="formtext">Pass</span>
<input type="password" name="epadPass" id="epadPass" required>
<input type="submit" value="Ok" class="formbuton" name="formbuton">
<br>
<span class="formtext">IP Adress : <?php echo $ip; ?></span>
<br>
<span class="formtext">Attempt : <?php echo $_SESSION['attempt'] ?></span>
</fieldset>
</form>
</div>
</div>
<?php require('../template/footer.php'); ?>
control.php
<?php
if (!isset($_SESSION)) {
session_start();
}
require('../function/start.php');
$title = 'Control';
if (isset($_POST['formbuton'])){
$name = htmlentities($_POST['epadName']);
$pwd = htmlentities($_POST['epadPass']);
}
$check = $db->prepare('SELECT user, pass FROM users');
$check->execute();
$result = $check->fetch(PDO::FETCH_ASSOC);
$user = $result['user'];
$pass = $result['pass'];
if ($name == $user && $pwd == $pass ){
$_SESSION['name']= $name;
header("location:main.php");
}else{
$_SESSION['attempt']--;
header('location:index.php');
}
?>
when a user enter the page(first visit) ; a session will be started, and attempt variable will be created. (index.php)
If they enter false data attempt variable will be decreased. (control.php)
if there are 3 failed attempt page will redirects to login_error.page (index.php)
First Problem : Session variable is not changing.
Second Problem: Even If I enter correct data, the page directs to index.php (login area) instead of main.php

Answer 1

try to place session_start(); at the first line, after <?php

Answer 2

I've solved the problem;
Actually I don't understand why
if(!isset($_SESSION){session_start; $_SESSION['attempt']=3;}
didn't work but when I modified this code to that code
session_start;
if (!isset($_SESSION['attempt']){$_SESSION['attempt']=3;}
Anyway, thank you for reading.