Sign up function working on one script but not another - php

Question

I have a sign up function on a script and I've copied it over to a new project and changed the variables - form inputs, table/database names etc. and the script won't do anything.
Signup.php
<form class="form" action="register.php" method="POST" enctype="application/x-www-form-urlencoded">
<input type="text" value="" placeholder="Username" id="username" name="username" />
<input type="text" value="" placeholder="Email" id="Email" name="Email" />
<input type="password" value="" placeholder="Password" id="password" name="password" />
<input type="submit" id="signin" name="submit" />
</form>
Register.php
<?php
include('connectivity.php');
if (mysqli_connect_errno())
{
echo "Failed to connect to mysqli: " . mysqli_connect_error();
}
else
{
}
function newUser()
{
include ('connectivity.php');
$username = $_POST['username'];
$username_escaped = mysqli_real_escape_string ($db, $username);
$email = $_POST['email'];
$email_escaped = mysqli_real_escape_string ($db, $email);
$password = sha1($_POST['password']);
$password_escaped = mysqli_real_escape_string ($db, $password);
$query = "INSERT INTO users (username, email, password) VALUES ('$username_escaped', $email_escaped', '$password_escaped')";
include('connectivity.php');
$data = mysqli_query ($db, $query)or die(mysqli_error($db));
if($data)
{
}
}
function SignUp()
{
if(!empty($_POST['email']))
{
include('connectivity.php');
$query = mysqli_query ($db, "SELECT * FROM users WHERE email = '$_POST[email]'")
or die(mysqli_error());
if(!$row = mysqli_fetch_array($query))
{
newUser();
echo ("<SCRIPT LANGUAGE='JavaScript'>
window.alert('User Registration Successful')
window.location.href='login.php';
</SCRIPT>");
}
else
{
echo ("<SCRIPT LANGUAGE='JavaScript'>
window.alert('You are already a registered user!')
window.location.href='homepage.html';
</SCRIPT>");
}
}
}
if(isset($_POST['submit']))
{
SignUp();
}
?>
The form when submitted just goes to the blank php page (register.php) - no window alert messages pop up and no redirection occurs.
This script works perfectly on my other form, can anybody see why it doesn't work on this form?
Cheers for reading!

Answer 1

$_post['email'] Doesnt exists because you have set the name attribute to "Email"
Edit:
I forgot to mention the essence of my answer. the name and $_POST are case sensitive, so "email" != "Email"

Answer 2

try this:
$query = mysqli_query ($db, "SELECT * FROM users WHERE email = '$email'") or die(mysqli_error($db));