Display Users Information with MySQL and PHP - php

Question

I am having problems displaying my users information that they inputted at sign up once they have logged in again. Once I sign up the information will be displayed properly on my account page but when I log out and log back in the information disappears. How can I access the information for when my users login?
This is my user sign up.
<?php
include 'global_settings.php';
function NewUser() {
$firstName = $_POST['firstName'];
$lastName = $_POST['lastName'];
$email = $_POST['email'];
$username = $_POST['username'];
$password = $_POST['password'];
$query = "INSERT INTO userlogin (firstName, lastName, email, username, password) VALUES ('$firstName', '$lastName', '$email', '$username', '$password')";
$data = mysql_query ($query)or die(mysql_error());
if($data) {
session_start();
$_SESSION["firstName"] = $firstName;
$_SESSION["lastName"] = $lastName;
$_SESSION["userName"] = $username;
$_SESSION["email"] = $email;
header("Location: ../chooseyoursport.php");
}
}
NewUser();
function SignUp() {
if(!empty($_POST['username'])){ //checking the 'user' name which is from Sign-Up.html, is it empty or have some text
$query = mysql_query("SELECT * FROM userlogin WHERE Username = $username AND Password = $password") or die(mysql_error());
if(!$row = mysql_fetch_array($query) or die(mysql_error())) {
newuser();
} else {
echo "SORRY...YOU ARE ALREADY REGISTERED USER...";
}
}
}
if(isset($_POST['submit'])) {
SignUp();
}
?>
This is my user login.
<?php
error_reporting(0);
session_start();
include 'global_settings.php';
//Convert POST to normal variables
$password = $_POST['password'];
$username = $_POST['username'];
$sql = mysql_query("SELECT * FROM userlogin WHERE Username='$username' AND Password='$password'");
$login_check = mysql_num_rows($sql);
// if login_check is greater than 0 then it will register a session (meaning if the user exists username and password are both correct)
if($login_check > 0){
while($row = mysql_fetch_array($sql)){
foreach( $row AS $key => $val){
$$key = stripslashes($val);
}
session_start();
$_SESSION["firstName"] = $firstName;
$_SESSION["lastName"] = $lastName;
$_SESSION["userName"] = $username;
$_SESSION["email"] = $email;
header("Location: ../chooseyoursport.php");
//echo "It worked";
}
} else {
echo "You could not be logged in! Either your username or password is incorrect <br> Please try again!";
}
?>

Answer 1

1) $$key = stripslashes($val); Double $$
2) Data which you are putting into $_SESSION is empty;
3) session_start(); 2 times in one program's space
4) And everything else that the guys have said above
foreach( $row AS $key => $val){
$$key = stripslashes($val);
}
session_start();
$_SESSION["firstName"] = $firstName;
$_SESSION["lastName"] = $lastName;
$_SESSION["userName"] = $username;
$_SESSION["email"] = $email;
header("Location: ../chooseyoursport.php");