提交按钮下载代码

我试图将表单数据保存到mysql数据库最近2天，然而，表单数据没有保存到mysql数据库，而是每次我按提交按钮时，它都会下载用户信息。php代码文件到我的计算机。需要帮助!这是html表单;

<form class="form-horizontal" role="form" action="User Info.php" method="post"/>
    <div class="form-group">
      <label class="control-label col-sm-2" for="First Name">First Name:</label>
      <div class="col-sm-10">
        <input type="text" name="FirstName" class="form-control" id="First Name"  placeholder="First Name">
      </div>
    </div>
    <div class="form-group">
      <label class="control-label col-sm-2" for="Last Name">Last Name:</label>
      <div class="col-sm-10">
        <input type="Last Name" name="LastName" class="form-control" id="Last Name" placeholder="Last Name">
      </div>
    </div>
    <div class="form-group">
      <label class="control-label col-sm-2" for="Company Name">Company Name:</label>
      <div class="col-sm-10">
        <input type="Company Name" name="CompanyName" class="form-control" id="Company Name" placeholder="Company Name">
      </div>
    </div>
    <div class="form-group">
      <label class="control-label col-sm-2" for="email">Email:</label>
      <div class="col-sm-10">
        <input type="Email" name="Email" class="form-control" id="Email" placeholder="Email">
      </div>
    </div>
    <div class="form-group">
        <label class="control-label col-sm-2" for="Message">Message</label>
       <div class="col-sm-10"> 
        <textarea type="Message" name="Message" class="form-control" rows="3" columns="50" id="Message" placeholder="Message"></textarea></div>
        </div>
  <div class="form-group">
    <div class="col-sm-offset-2 col-sm-10">
    <button name="submit" class="submit-btn" type="submit">Submit</button>

这是php代码db.php;

<?php
    $conn = mysql_connect('localhost','root','....', 'testforlivesite') or die("error while connecting to the database");
    $db = mysql_select_db('testforlivesite', $conn) or die("error while connecting to the database");
?>

<?php
    include_once('db.php');
    $FirstName = $_POST['FirstName'];
    $LastName = $_POST['LastName'];
    $CompanyName = $_POST['CompanyName'];
    $Email = $_POST['Email'];
    $Message = $_POST['Message'];
    if(mysql_query("INSERT INTO ContactUs (FirstName, LastName, CompanyName, Email, Message) VALUES ('$FirstName', '$LastName', '$CompanyName', '$Email', '$Message')"))
        echo "Thanks for contacting!";
    else 
        echo "Please rewrite the message.";
?>