configure remote connection for multiple instances sql server 2008
You need to start the SQL Browser service to enable connections to named instances. 

Explanation here:


  Upon startup, SQL Server Browser starts and claims UDP port 1434. SQL
  Server Browser reads the registry, identifies all instances of SQL
  Server on the computer, and notes the ports and named pipes that they
  use. When a server has two or more network cards, SQL Server Browser
  returns the first enabled port it encounters for SQL Server. SQL
  Server Browser support ipv6 and ipv4.