Form action help

[Duckface]

It's this page you see:

http://spawnscape614.co.uk/forums/reportuser.php?

And I'm trying to validate the first input for a test. And when clicking the send report button it simply reloads...
Appropriate html:

<form class="vbform block" action="{vb:raw _SERVER.PHP_SELF}">
<label for="username">Enter offender's name: </label>
				<input type="text" class="primary textbox" id="name" name="username" tabindex="1" /></input><span class="error"> * <?php echo $usernameErr;?></span>
<input type="submit" class="button" value="Send Report" tabindex="1"  />
</form>

Appropriate php:

PHP Code:

$usernameErr = "";
$username = "";
if(isset($_POST['submit'])) {
   if (empty($_POST["name"])) {
     $nameErr = "Name is required";
   } else {
     $name = test_input($_POST["name"]);
   }
   
}

   function test_input($data) {
   $data = trim($data);
   $data = stripslashes($data);
   $data = htmlspecialchars($data);
   return $data;
} 


--------------- Added [DATE]1435933147[/DATE] at [TIME]1435933147[/TIME] ---------------

Idk why it just reloads. And I tried the var instead of the raw and it didn't work.