get connection string from web.config in asp.net 3.5 is different from ASP.Net 1.1. Below the code to declare connectionstring in our web.config file.
In Asp.Net 2.0 and Asp.Net 3.5 we have new Tag Inside Web.config file that is ConnectionString Tag
<add name="MyConnectionString" connectionString="Server=ServerName;Database=YourDBName;Uid=YOURUSerId;Pwd=YourDBPassword;"/>
Now to get the Connection string defined in the web.config file you have to do like this in your .cs file below code is based on c#
string Conn= ConfigurationManager.ConnectionStrings["MyConnString"].ConnectionString;
Dim Conn as String = ConfigurationManager.ConnectionStrings("MyConnString").ConnectionString