Submit form without Refreshing Page using Ajax and Jquery

<center>
<div style="width:620px; padding:10px; border:10px solid #F6F6F6;">

<div style="width:600px;float:left;padding:10px;" align="left"><div id="submit_without_page_refresh_status" style="font-family: helvetica, arial, 'lucida grande', sans-serif; font-size:12px; color:black;"></div></div><br clear="all">

<div style="width:100px;float:left;padding:10px;padding-top:16px;font-family: helvetica, arial, 'lucida grande', sans-serif; font-size:12px; color:black;" align="left">Your Fullname:</div>
<div style="width:400px;float:left;padding:10px;" align="left"><input type="text" id="fullname" class="location_to_send_files"></div><br clear="all">

<div style="width:100px;float:left;padding:10px;padding-top:16px;font-family: helvetica, arial, 'lucida grande', sans-serif; font-size:12px; color:black;" align="left">Email Address:</div>
<div style="width:400px;float:left;padding:10px;" align="left"><input type="text" id="email" class="location_to_send_files"></div><br clear="all">

<div style="width:100px;float:left;padding:10px;font-family: helvetica, arial, 'lucida grande', sans-serif; font-size:12px; color:black;" align="left">Your Comment:</div>
<div style="width:400px;float:left;padding:10px;" align="left"><textarea id="comment" class="location_to_send_files" style="width:300px; height:100px;"></textarea></div><br clear="all">

<div style="width:100px;float:left;padding:10px;font-family: helvetica, arial, 'lucida grande', sans-serif; font-size:12px; color:black;" align="left">&nbsp;</div>
<div style="width:400px;float:left;padding:10px;" align="left"><button style="width:80px; padding:8px; cursor:pointer;" onClick="submit_without_page_refresh();">Submit</button></div><br clear="all">

</div>
</center>

<script language="javascript" type="text/javascript" src="jquery-1.8.2.min.js"></script>
<script type="text/javascript">
function submit_without_page_refresh()
{
      //alert("YES SIR");
      var reg = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;
      var fullname = $("#fullname").val();
      var email = $("#email").val();
      var comment = $("#comment").val();

      if(fullname == "")
      {
            $("#submit_without_page_refresh_status").html('<div class="notice" align="left">Please enter your fullname to get started.</div>');
            $("#fullname").focus();
      }
      else if(email == "")
      {
            $("#submit_without_page_refresh_status").html('<div class="notice" align="left">Please enter your email address to proceed.</div>');
            $("#email").focus();
      }
      else if(reg.test(email) == false)
      {
            $("#submit_without_page_refresh_status").html('<div class="notice" align="left">Please enter a valid email address ya.</div>');
            $("#updates_subscription").focus();
      }
      else if(comment == "")
      {
            $("#submit_without_page_refresh_status").html('<div class="notice" align="left">Please enter your comment to go.</div>');
            $("#comment").focus();
      }
      else
      {
            var dataString = 'fullname='+ fullname + '&email='+ email + '&comment='+ comment;
            $.ajax({
                  type: "POST",
                  url: "submit_form_without_page_refresh.php",
                  data: dataString,
                  cache: false,
                  beforeSend: function()
                  {
                       $("#submit_without_page_refresh_status").html('<div style="padding-left:100px;"><img src="loading.gif" alt="Sending...." align="absmiddle" title="Sending...."/> <font style="font-family: helvetica, arial, 'lucida grande', sans-serif; font-size:12px; color:black;">Please wait...</font></div><br clear="all">');
                  },
                  success: function(response)
                  {
                        $("#submit_without_page_refresh_status").html($(response).fadeIn(2000));
                        $("#fullname").val('');
                        $("#email").val('');
                        $("#comment").val('');
                  }
            });
      }
}
</script>

<?php
if(isset($_POST["fullname"]) && isset($_POST["email"]) && isset($_POST["comment"]) && !empty($_POST["fullname"]) && !empty($_POST["email"]) && !empty($_POST["comment"]))
{
?>
<center>
<div style="width:600px; font-family: helvetica, arial, 'lucida grande', sans-serif; font-size:12px; color:black;" align="left">
<b>Your Fullname:</b> <?php echo strip_tags($_POST["fullname"]); ?><br><br>
<b>Email Address:</b> <?php echo strip_tags($_POST["email"]); ?><br><br>
<b>Your Comment:</b> <?php echo nl2br(strip_tags($_POST["comment"])); ?><br><br>

</div>
</center>
<?php

}
else
{
echo '<div class="notice">Sorry, some thing went wrong and your submission was unsuccessful. Please try again or contact the site admin to report this error should the problem persist. Thanks...</div>';
}
?>