Go tho this link : http://www.w3schools.com/html/default here you can get tips and samples.

First of all tell us your project is in c#.net or vb.net and is it window application or webapplication. And NullReferenceException generate when you assign null value to which variable are not accept this value.

Can you change your connection string. Ans what error you see when you try to run fro other system.