Your connection string is not good. You have to either specify user name and password or set it to use trusted connection (check here for proper syntax: http://www.connectionstrings.com/sql-server-2008
], supposing SQL 2008; but there you can find other versions of SQL server and other datasources too).
Could be this:
private string connectionstring =@"Server=NARASIMAN;Database=master;Trusted_Connection=True;";