Php mysql html form submission error

Question

I'm working on a cms for my site and this form is not submitting. I know its a query problem, but I can't figure out whats wrong. Any help? Also, the $db is in my config and I do include it at the top of the page. The problem is its not submitting and all it does it refresh, nothing else. I also want to display there form submissions in a table later, but I don't know how to do that, if anyone can help me with that part that would be great as well.

php:

    <?php
if(isset($_POST['submit']))
{
  $c_name = $_POST['channel_username'];
  $v_link = $_POST['video_link'];
  $v_title = $_POST['video_title'];
  $v_desc = $_POST['vido_description'];
  $v_tags = $_POST['video_tags'];
  $m_sources = $_POST['music_sources'];
  $s_requests = $_POST['special_requests'];

  if(empty($c_name) or empty($v_link) or empty($v_title) or empty($v_title) or empty($v_desc) or empty($v_tags))
  {
    echo 'You must fill in the first 5 fields.';
  }
  else
  {
    $getRank = $db->query("SELECT * FROM users WHERE username = '".$_SESSION['username']."'");
    while ($row = $getRank->fetch_assoc())
    {
      $usename = $row['username'];
      $rank = $row['rank'];
    }
   $db->query("INSERT INTO submitted_forms (username, rank, channel_username, video_link, video_title, video_description, video_tags, music_sources, special_requests) VALUES ('$username', '$rank', '$c_name', '$v_link', '$v_title', '$v_desc', '$v_tags', '$m_sources', '$s_requests')");
    echo 'Form submitted successfully.';
    }
  }
?>

Html:

    <form method="POST">
  <p>Channel name <input type="text" name="channel_name" required>*</p>
  <p>Video Link   <input type="text" name="video_link" required>*</p>
  <p>Video Title  <input type="text" name="video_title" required>*</p>
  <p>Video Description <input type="text" name="video_description" required>*</p>
  <p>Video Tags   <input type="text" name="video_tags" required>*</p>
  <p>Music Sources <input type="text" name="music_sources"></p>
  <p>Special Requests <input type="text" name="special_requests"></p>
  <br></br>
  <p><input type="submit" name="submit" value="Submit"></p>
</form>

Answer 1

If the problem is indeed with the query, then it's probably this:

$db->query("INSERT INTO submitted_forms (username, rank, channel_username, video_link, video_title, video_description, video_tags, music_sources, special_requests) VALUES (''.$username.'', ''.$rank.'', ''.$c_name.'', ''.$v_link.'', ''.$v_title.'', ''.$v_desc.'', ''.$v_tags.'', ''.$m_sources.'', ''.$s_requests.'')");

I think instead, you want:

$db->query("INSERT INTO submitted_forms (username, rank, channel_username, video_link, video_title, video_description, video_tags, music_sources, special_requests) VALUES ('$username', '$rank', '$c_name', '$v_link', '$v_title', '$v_desc', '$v_tags', '$m_sources', '$s_requests')");

-- edit --

further to that, although it won't give you an error as-is, you really oughtn't insert fresh POST data in there. At the very least you probably want to use mysqli_real_escape_string on it.