An object-oriented programming language developed by Microsoft that can be used in .NET.
How should I avoid this I mean I want to use different "PC-name" & "User-Name" on new system. Note that my Sql Login credentials are same in both New & Old PC still it won't let me login.
I'm not sure that I get this. First you say that you want to use different user-names, and then you say that your SQL login credentials are the same in both?
Are you using Windows authentication or SQL authentication? What does your connection string look like?
If you look in the SQL Server errorlog, you will find more details on why connection failed.