无法打开到sql server的连接[xampp]

I installed the "PHP for SQL Server" and " ODBC Driver 11"

but then I got this message.

Connection could not be established. Array ( [0] => Array ( [0] => 08001 [SQLSTATE] => 08001 [1] => 67 [code] => 67 [2] => [Microsoft][ODBC Driver 11 for SQL Server]Named Pipes Provider: Could not open a connection to SQL Server [67]. [message] => [Microsoft][ODBC Driver 11 for SQL Server]Named Pipes Provider: Could not open a connection to SQL Server [67]. ) [1] => Array ( [0] => HYT00 [SQLSTATE] => HYT00 [1] => 0 [code] => 0 [2] => [Microsoft][ODBC Driver 11 for SQL Server]Login timeout expired [message] => [Microsoft][ODBC Driver 11 for SQL Server]Login timeout expired ) [2] => Array ( [0] => 08001 [SQLSTATE] => 08001 [1] => 67 [code] => 67 [2] => [Microsoft][ODBC Driver 11 for SQL Server]A network-related or instance-specific error has occurred while establishing a connection to SQL Server. Server is not found or not accessible. Check if instance name is correct and if SQL Server is configured to allow remote connections. For more information see SQL Server Books Online. [message] => [Microsoft][ODBC Driver 11 for SQL Server]A network-related or instance-specific error has occurred while establishing a connection to SQL Server. Server is not found or not accessible. Check if instance name is correct and if SQL Server is configured to allow remote connections. For more information see SQL Server Books Online. ) )

The connection code I'm using

$serverName = "localhost/sqlexpress"; //serverName\instanceName
$connectionInfo = array( "Database"=>"company", "UID"=>"root", "PWD"=>"");
$conn = sqlsrv_connect( $serverName, $connectionInfo);

if( $conn ) {
    echo "Connection established.<br />";
}else{
    echo "Connection could not be established.<br />";
    die( print_r( sqlsrv_errors(), true));
}

Please help, it's the first time using sql server so I don't know what to do !