Classic ASP connecttion string to SQL Express

Question

I have ASP pages that connect to SQL Server (10.50.1400) with the connection string

conn.Open ("DRIVER={SQL Server};SERVER=svr;UID=ui;PWD=pw;DATABASE=db");

but recently was installed an EXPRESS instance and my pages ASP start don't connect to SQL Server (10.50.4000) database. I changed my connection string to

conn.Open ("DRIVER={SQL Server};SERVER=svr\EXPRESS;UID=ui;PWD=pw;DATABASE=db");

but still don't work. Also (googling) I changed to

conn.Open ("Provider=SQLOLEDB;SERVER=svr;UID=ui;PWD=pw;DATABASE=db");

but the same. The error that "SQL Server don't exist or connection refused".

Any help, please. Thanks!