How to fix session not starting after unsetting a variable

Please I have been trying to fix this but not working out right for me. I have a session started but after logging out using unset($_SESSION['variable'], I am unable to login back as the session is not setting.

Please help me out. Note: I am unable to login after unsetting the variable.

//this is login.php
<?php
    session_start();
    ob_start();
    $msg = "";
    if (isset($_POST['login'])){
        include "dbconnect.php";
        if($_SESSION['emaill'] !== NULL){
            $emaill= $_SESSION['emaill'];
            $passWord = $_POST['passWord'];
            if (empty($emaill && $passWord) == false){
                $sql = "SELECT * FROM `sono` WHERE `eMail`='$emaill' && `passWord`='$passWord'";
                $check = mysqli_query($dbconnect, $sql) or die (mysqli_error($dbconnect));
                $result = mysqli_num_rows($check);
                if ($result > 0){
                    $emaill= $_SESSION['emaill'];
                    header ('location: home.php');
                    exit();
                } else
                    $msg = "<p style='color: red; padding-left: 10px'>Invalid password or email address</p>";
            } else
                $msg = "<p style='color: red; padding-left: 10px'>Please enter your email and password to login</p>";
        } else
            $msg = "<p style='color: red; padding-left: 10px'>My scripts not working yet</p>";
    }
?>

// this is for logout
<?php
    session_start();
    if (isset($_SESSION['emaill'])){
        unset($_SESSION['emaill']);
        header('location: login.php');
    }
?>