Cannot register default instance MSSQLSERVER in SQL Server 2008

Question

I have installed SQL Server 2008 Developer on Windows 7 (64 bit). In SQL Management Studio I cannot register the default instance MSSQLSERVER. It cannot find it although the

Answer 1

I always connected as:

[machine_name]/[instance_name]

and it wasn't able to connect. What works is connecting simply as:

[machine_name]

This is probably due to the fact that I am running a DEFAULT instance.