コード全体を表示するだけです。次のクエリはすべて機能しています。
    <?php
$errorMsg = "";
$x1 = "";
$x2 = "";
$x3 = "";
$x4 = "";
$email = "";
$password = "";
$x7= "";
if (isset ($_POST['x1'])){
     $x1 = $_POST['x1'];
     $x2 = $_POST['x2'];
     $x3 = $_POST['x3'];
     $x4 = $_POST['x4'];
     $email = $_POST['email'];
     $password = $_POST['password'];
     $x7= $_POST['x7'];
         $x1 = stripslashes($x1);
     $x2 = stripslashes($x2);
         $x3 = stripslashes($x3);
     $x4 = stripslashes($x4);
     $email = stripslashes($email);
     $password = stripslashes($password);
     $x7= stripslashes($x7);
         $x1 = strip_tags($x1);
     $x2 = strip_tags($x2);
     $x3 = strip_tags($x3);
     $x4 = strip_tags($x4);
     $email = strip_tags($email);
     $password = strip_tags($password);
     $x7= strip_tags($x7);
     include_once "scripts/connect_to_mysql.php";
     $emailCHecker = mysql_real_escape_string($email);
     $emailCHecker = eregi_replace("`", "", $emailCHecker); 
     $sql_email_check = mysql_query("SELECT email FROM tablename WHERE email='$emailCHecker'"); 
     $email_check = mysql_num_rows($sql_email_check); 
     if ((!$x1) || (!$x2) || (!$x3) || (!$x4) || (!$email) || (!$password) || (!$x7)) { 
     $errorMsg = 'following issues are missing<br />';
    if(!$x1){ 
       $errorMsg .= ' *x1<br />'; 
     } 
     if(!$x2){ 
       $errorMsg .= ' *x2<br />';
     } 
     if(!$x3){ 
       $errorMsg .= ' *x3<br />';
     } 
     if(!$x4){ 
       $errorMsg .= ' *x4<br />'; 
     } 
     if(!$email){ 
       $errorMsg .= ' *email<br />'; 
     }
     if(!$x7){ 
       $errorMsg .= ' *x7<br />'; 
     }  
     } else if ($email_check > 0){ 
       $errorMsg = "Mail already exists"; 
     } else 
     { 
     $x1 = mysql_real_escape_string($x1);
     $x2 = mysql_real_escape_string($x2);
     $x3 = mysql_real_escape_string($x3);
         $x4 = mysql_real_escape_string($x4);
     $email = mysql_real_escape_string($email);
     $password = mysql_real_escape_string($password);
     $x1 = eregi_replace("`", "", $x1);
     $x2 = eregi_replace("`", "", $x2);
     $x3 = eregi_replace("`", "", $x3);
     $x4 = eregi_replace("`", "", $x4);
     $email = eregi_replace("`", "", $email);
     $db_password = md5($password); 
     $sql = mysql_query("INSERT INTO tablename (x1, x2, x3, x4, sign_up_date, email, password)    
     VALUES('$x1','$x2','$x3','$x4', now(), '$email','$db_password')")  
     or die (mysql_error()); 
     $id = mysql_insert_id();
     /*mkdir("members/$id", 0755); */
    $to = "$email"; 
    $from = "xxx@xxx.xx";       
    $subject = "activationlink";        
    $message = "Link for activation";
    $headers  = "From: $from\r\n";
    $headers .= "Content-type: text\r\n";
    mail($to, $subject, $message, $headers);
   $msgToUser = "text";
   /*include_once 'msgToUser.php';  */
   exit();
   } 
} else { 
      $errorMsg = "Errormessages";
          $x1 = "";
      $x2 = "";
      $x3 = "";
      $x4 = "";
      $email = "";
      $password = "";
      $x7 = "";
}
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>XXXX</title>
        <link rel="stylesheet" href="css/colorbox.css" />
        <script type="text/javascript" src="js/jquery-1.7.1.min.js"></script> 
        <script type="text/javascript" src="js/jquery.colorbox.js"></script>   
<?php if **a variable or clause will be true: ?>
        <script type="text/javascript">
        $(document).ready(function(){
        $.colorbox({iframe:true, scrolling:false, href:"#$msgToUser.php", innerWidth:"408px", innerHeight:"292px", opacity:0.75, overlayClose:false, escKey:false, });
        });
        $("#colorboxCloseBtn").click(function() {
        $.colorbox.close();
        });
        $(document).ready(function() {
        /* Automatically resize to content 
        var y = $(document.body).height();
        var x = $(document).width();
        parent.$.colorbox.resize({innerWidth:x, innerHeight:y});*/
        $("#button_cancel").click(function() {
        parent.$.colorbox.close();
        return false;
        })
        });
        </script> 
 <?php endif; ?>