In the example below I am wanting to do all of the 'safety' checks on the $_POST variables but it seems when I click submit I get a white page why? I am wanting it to show the errors etc

Form Process:

/* check if the form is submitted  */ 
if (isset($_POST['submitButton'])) { 

    $fullName = $_POST['fullname'];

    if($_SERVER['REQUEST_METHOD'] == 'POST' && !empty($fullName))
    {
        if (!ctype_alpha(str_replace(array("'", "-"), "",$fullName))) { 
            $errorfullName .= '<span class="errorfullName">*First name should be alpha characters only.</span>';
        }

        if (strlen($fullName) < 3 OR strlen($fullName) > 40) {
            $errorfullName .= '<span class="errorfullName">*First name should be within 3-40 characters long.</span>';
        }
    }
}