session - PHP logging in redirection -

i'm working on site , when try login, automatically redirects me login page not allowing me login. think sessions, not sure. if please take me. dashboard based site supposed redirect user there correct dash`board there rank, seems not working. heres login page:

login:

    <?php require 'core/config.php';  if(isset($_post['submit'])) {     $username = $db->real_escape_string($_post['username']);     $password = md5($_post['password']);      if(empty($username) or empty($password))     {         echo 'you must fill in both boxes!';     } else {         $query = $db->query("select * users username = '".$username."'");         while($row = $query->fetch_array())         {             $dbpassword = $row['password'];         }          if($password !== $dbpassword)         {             echo 'password incorrect.';         } else {             $query1 = $db->query("select * users username='".$username."'");             while($rows = $query1->fetch_array())             {                 $rank = $rows['rank'];             }              if($rank === 'admin')             {                 $_session['admin'] = '1';                 $_session['username'] = $username;                  echo '<script>window.location="admin/index.php";</script>';             }             elseif ($rank === 'partner')             {                 registersession('partner', '1');                 registersession('username', $username);                  header('location: partner/');             }             elseif ($rank === 'trainee')             {                 registersession('trainee', '1');                 registersession('trainee', '1');                  header('location: trainee/');             }             else              {                 echo 'you aren\'t member.';             }         }     } } ?> 

code redirect if not logged in:

<?php session_start(); if(isset($_session['partner'])) { $_session['username'];  } else { header("location: ../index.php") } ?> 

seems session variable partner not being set. so

instead of

registersession('partner', '1'); registersession('username', $username); 

make use of

$_session['partner']=1; $_session['username']=$username; 

try add session_start(); ob_start(); on top of config.php file.