Where can you connect from?

locally on the server but not from a remote machhine then it wold indicate that either a fire wall (or a router with an access control list) is blocking you.

If you cant log in locally on the server look at the event logs and the error log (C:\Program Files\Microsoft SQL Server\MSSQL10.MSSQLSERVER\MSSQL\Log or some similar place) and see if you get an error.

If its from only a certain type of application then have a look at the connection string.

As an aside what did you change the port number from and to?