i have a problem creating my login page. i don't know the problem is. please help!

//index.php
<?php
require 'core.inc.php';
require 'connect.inc.php';

if (loggedin()){
echo 'You are logged in.';
}else{
include 'login.inc.php';
}

?>

//login.inc.php
if(isset($_POST['username']) && isset($_POST['password'])){
    $username=$_POST['username'];
    $password=$_POST['password&'];

if(!empty($username) && !empty($password)){
        $query="SELECT * FROM users WHERE username=$username AND password=$password";
if($query_run=mysql_query($query)){
    $query_num_rows=mysql_num_rows($query_run);
    if(query_num_rows==0){
        echo 'Invalid username and password combination.';
    }else if($query_num_rows==1){
     $user_id=mysql_result($query_run,0,'id');
        $_SESSION['user_id']=$user_id;
        header('Location: index.php');
    }
}

    }else{
        echo 'You must supply a username and password';
    }
}
?>

<form action="<?php echo $current_file; ??>" method="POST">
Username: <input type="text" name="username">
Password:<;input type="password" name="password">
<input type="submit" value="Log in">
</form>

//connect.inc.php

    $mysql_host="localhost";
    $mysql_username=";root";
    $mysql_password="";

    $mysql_db="dbase";

    if(!mysql_connect($mysql_host,$mysql_username,$mysql_password) || !mysql_select_db($mysql_db)){
        die(mysql_error());
    }
?>

//core.inc.php

ob_start();
session_start();
$current_file = $_SERVER['SCRIPT_NAME'];

function loggedin(){
    if(isset($_SESSION['user_id'])&&!empty($_SESSION['user_id'])){
        return true;
    }else{
        return false;
    }

}

?>