Dynoblox Login.php

<?php
    include "Header.php";

    if (!$User) {

        $Username = SecurePost($_POST['Username']);
        $Password = SecurePost($_POST['Password']);
        $Submit =   SecurePost($_POST['Submit']);

        if ($Submit) {

            if (!$Username || !$Password) {

                echo "
                <div id='Error'>
                    Sorry, you have missing fields.
                </div>
                ";

            }

            else {

                $_HASH = hash('sha512',$Password);

                $checkUser = mysql_query("SELECT * FROM Users WHERE Username='$Username'");

                $cU = mysql_num_rows($checkUser);

                if ($cU == 0) {

                echo "
                <div id='Error'>
                    Sorry, that account does not exist.
                </div>
                ";

                }

                else {

                    $getPassword = mysql_query("SELECT * FROM Users WHERE Username='$Username' AND Password='$_HASH'");

                    $gP = mysql_num_rows($getPassword);

                    if ($gP == 0) {

                        echo "
                        <div id='Error'>
                            Sorry, but your password is incorrect.
                        </div>
                        ";

                    }

                    else {

                        $_SESSION['Username']=$Username;
                        $_SESSION['Password']=$_HASH;

                        header("Location: http://www.dynoblox.cf/home.html");

                    }

                }
}

        }

        echo "
        <div class='row'>
<div class='col s12 m3 l2'>&nbsp;</div>
<div class='col s12 m12 l8'>
<div style='padding-top:50px;'></div>
<div class='container' style='width:100%;'>
<div class='center-align'>
<div style='padding-bottom:50px;'>
<div class='text-center'>
</div>
</div>
</div>
<div class='row'>
<div class='col s12 m12 l4'>&nbsp;</div>
<div class='col s12 m12 l4'>
<div class='bc-content center-align'>
<h4 style='padding-bottom:25px;'>Log in</h4>
<form action='' method='POST'>
<div class='input-field'>
<input type='text' name='Username' id='Username'>
<label for='username' class=''>Username</label>
</div>
<div class='input-field'>
<input type='password' name='Password' id='Password'>
<label for='password'>Password</label>
</div>
<div class='input-field'>
<i class='waves-effect waves-light btn blue waves-input-wrapper' style=''>&nbsp;<input type='submit' name='Submit' class='waves-button-input' value='LOG IN'>&nbsp;</i>
</div>
</form>
</div>
</div>
</div>
</div></div></div>
        ";

    }

    else {

        echo "
<div id='Login'>
                    <left>
                        <b>Welcome, $User!</b>
                        <br />
                        <br />
                        <img src='YOUR SITE LINK/AVATAR THING.php?ID=$myU->ID'>
                                                <center position:absolute; TOP:35px; LEFT:170px; WIDTH:50px; HEIGHT:50px>
                                               <b>Welcome to Dynoblox!</b>
                                                <br />
                        <br />
                         DESC THING
                    </center>

                </div>
                ";

            }
            echo "

            ";
            ?>
            </td>
        </tr>
    </table>
</div>
</form>
<?php
include('Footer.php');