Anyone cn help fix this code. Submit button nt evn clicking. Whts wrong. Thanks

<?php
include_once("php_includes/check_login_status.php");
if($user_ok == true) {
$u=$log_username;

}
$sql = "SELECT * FROM users WHERE username='$u' AND activated='1' LIMIT 1";
$user_query = mysqli_query($db_conx, $sql);
// Fetch the user row from the query above
while ($row = mysqli_fetch_array($user_query, MYSQLI_ASSOC)) {

$gender = $row["gender"];
}

// Ajax calls this REGISTRATION code to execute
if(isset($_POST["f"])){
// CONNECT TO THE DATABASE
// GATHER THE POSTED DATA INTO LOCAL VARIABLES
$f = preg_replace('#[^a-z0-9]#i', '', $_POST['f']);
$l = preg_replace('#[^a-z0-9]#i', '', $_POST['l']);
$wt= preg_replace('#[^a-z ]#i', '', $_POST['wt']);
$a= preg_replace('#[^a-z ]#i', '', $_POST['a']);
$ws= preg_replace('#[^a-z ]#i', '', $_POST['ws']);
$c = preg_replace('#[^a-z ]#i', '', $_POST['c']);

// FORM DATA ERROR HANDLING
if($f == "" || $l == "" || $wt || $a == "" || $ws || $c == "" ){
echo "The form submission is missing values.";
exit();
} else {

// Add user info into the database table for the main site table

$sql = "UPDATE users SET firstname='$f', lastname ='$l', wagsbooty ='$wt', abs ='$a', wagsboobs ='$ws', crash ='$c' WHERE username='$u' LIMIT 1";

$query = mysqli_query($db_conx, $sql);
$uid = mysqli_insert_id($db_conx);
echo "startup_success";
exit();
}
exit();
}


?>

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Sign Up</title>
<link rel="icon" href="favicon.ico" type="image/x-icon">
<link rel="stylesheet" href="style/style.css">
<style type="text/css">
#startupform{
margin-top:24px;
}
#startupform > div {
margin-top: 12px;
}
#startupform > input,select {
width: 200px;
padding: 3px;
background: #F3F9DD;
}
#startupbtn {
font-size:18px;
padding: 12px;
}

</style>
<script src="js/main.js"></script>
<script src="js/ajax.js"></script>
<script>

function emptyElement(x){
_(x).innerHTML = "";
}

function startup(){
var f = _("firstname").value;
var l = _("lastname").value;
var wt = _("wagsbooty").value;
var a = _("abs").value;
var ws = _("wagsboobs").value;
var c = _("crash").value;

var status = _("status");
if(f == "" || l == "" wt || a == "" || ws || c == "" ){
status.innerHTML = "Fill out all of the form data";
} else {
_("startupbtn").style.display = "none";
status.innerHTML = 'please wait ...';
var ajax = ajaxObj("POST", "start_page1.php");
ajax.onreadystatechange = function() {
if(ajaxReturn(ajax) == true) {
if(ajax.responseText != "startup_success"){
status.innerHTML = ajax.responseText;
_("startupbtn").style.display = "block";
} else {
window.scrollTo(0,0);
_("startupform").innerHTML = "OK!";
}
}
}
ajax.send("f="+f+"&l="+l+"&wt="+wt+"&a="+a+"&ws="+ws+"&c="+c);
}
}

</script>
</head>
<body>
<?php include_once("template_pageTop.php"); ?>
<div id="pageMiddle">
<h3>Fill in this form to create your profile!</h3>
<form name="startupform" id="startupform" onsubmit="return false;">
<div>Firstname: </div>
<input id="firstname" type="text" onfocus="emptyElement('status')" maxlength="16">
<br /><br />
<div>Lastname: </div>
<input id="lastname" type="text" onfocus="emptyElement('status')" maxlength="16">
<br /><br />

<div>
<?php

if($gender === 'm'){
echo "WAG with hottest booty :";?></br>
<select id="wagsbooty" onfocus="emptyElement('status')" maxlength="255">
<?php include_once("template_wags_list.php");

}else{
echo "Star with hottest abs:";?></br>
<select id="abs" onfocus="emptyElement('status')" maxlength="255">
<?php include_once("template_abs_list.php");
}
?>
</select>
</div>
</br>
<div>
<?php
if($gender === 'm'){
echo "WAG with hottest boobs :";?></br>
<select id="wagsboobs" onfocus = "emptyElement('status')" maxlength="255">
<?php include_once("template_boobs_list.php");

}else{
echo "I have a crash on :";?></br>
<select id="crash" onfocus ="emptyElement('status')" maxlength="255">
<?php include_once("template_crash_list.php");
}
?>
</div>
</select>
</br>

</br>
<button id="startupbtn" onclick="startup()">Create Profile</button>
<span id="status"></span>
</form>
</div>
<?php include_once("template_pageBottom.php"); ?>
</body>
</html>