Correction svp !

<?php
if (isset($_POST["Valid"])) {$Valid =  $_POST["Valid"];

mysql_connect("127.0.0.1", "root", ""); mysql_select_db("Key_Computrace");

$req=mysql_query("select * from Key_Computrace where ExistKey='$Valid' and VerifKey='$Valid'"); // ExistKey = 1 | VerifKey = 1 = NO
$nb= mysql_num_rows($req); if ( $nb > 0 ) {header ('Location: KeyProduct.php'); }

$req=mysql_query("select * from Key_Computrace where ExistKey<>'$Valid'");  					// ExistKey = 0 | VerifKey = 0 = NO
$nb= mysql_num_rows($req); if ( $nb > 0 ) {header ('Location: KeyProduct.php'); }

$req=mysql_query("select * from Key_Computrace where ExistKey<>'$Valid' and VerifKey='0'");  	// ExistKey = 0 | VerifKey = 0 = NO
$nb= mysql_num_rows($req); if ( $nb > 0 ) {header ('Location: KeyProduct.php'); }

$req=mysql_query("select * from Key_Computrace where ExistKey='$Valid' and VerifKey='0'");  	// ExistKey = 1 | VerifKey = 0 = YES
$nb= mysql_num_rows($req); if ( $nb > 0 ) {
$req = mysql_query("INSERT INTO Key_Computrace ('VerifKey') VALUES ('$Valid'"); header ('Location: Validite.php'); }
}
?>