สอบถามคะ ระบบเป็น php + sql server มีปัญหาตรง connect คะ บ้างครั้งก็ connect ได้ บ้างครั้งก็ connect ไม่ได้

<?
$hostname = "localhost";
$dbuser = "sa";
$dbpassword = "1234";
$dbname = "db_test";
mysql_connect($hostname, $dbuser, $dbpassword) or die("Don't Connect Database");
mysql_select_db($dbname)or die("Don't Connect Database!!");
mysql_query("set NAMES tis620 ");
?>

$myServer = "ServerName";
$myUser = "user";
$myPass = "pass";
$myDB = "DBName"; 
$conn = new COM ("ADODB.Connection")or die("Cannot start ADO");
$connStr = "PROVIDER=SQLOLEDB;SERVER=".$myServer.";UID=".$myUser.";PWD=".$myPass.";DATABASE=".$myDB; 
$conn->open($connStr); //Open the connection to the database

$strSQL = " SELECT  FNAME,LNAME  FROM TableName  ";	
$objRec = $conn->Execute($strSQL);
          	While (!$objRec->EOF)
			{    
				echo  $objRec->Fields[FNAME]->Value ; 
                                echo  $objRec->Fields[LNAME]->Value ; 
                    }