联系表单返回空白页

我正在为游戏服务器制作一个小网站，我在制作联系表单时遇到了一些麻烦，当我点击提交时，它返回一个空白页面，不发送电子邮件。下面是代码，HTML和PHP

<form method="post" action="contact.php">
<div>
<div class="row">
<div class="6u">
<input type="text" name="senderName" id="name" placeholder="Nume" />
</div>
<div class="6u">
<input type="text" name="senderEmail" id="email" placeholder="E-mail" />
</div>
</div>
<div class="row">
<div class="6u">
<input type="text" name="senderUsername" id="name" placeholder="Username Minecraft" />
</div>
<div class="6u">
<input type="text" name="senderMethod" id="email" placeholder="Modalitate de plata (PayPal sau PaySafeCard)" />
</div>
</div>
<div class="row">
<div class="12u">
<textarea name="message" id="message" placeholder="Mesaj Optional (in caz ca vrei sa adaugi ceva)"></textarea>
</div>
</div>
<div class="row double">
<div class="12u">
<ul class="actions">
<li><input type="submit" value="Trimite" /></li>
<li><input type="reset" value="Reseteaza" class="alt" /></li>
</ul>
</div>
</div>
</div>
</form>

PHP:

if($_POST["submit"]) {
$recipient="outsidebbr@yahoo.com";
$subject="Test";
$senderName = $_POST['senderName']
$senderEmail = $_POST['senderEmail'] ;
$senderUsermame = $_POST['senderUsermame']
$senderMethod = $_POST['senderMethod']
$message = $_POST['message'] ;

mail( $recipient, $subject, "From: $senderEmail", $message);
header( "Location: form-thankyou.html" ); }
?>

有人能帮忙吗?谢谢!