At least one of them must be a named instance. So, open the SQL Server 2012 version of SQL Server Configuration Manager, and see what the services say (and make sure the one you want to connect to is started - you can right-click to do so). Mine are all named instances:
So, if I wanted to connect to the SQL Server 2008 SP3 instance, I would use any of the following to connect:
.\SQL2008SP3
LOCALHOST\SQL2008SP3
(local)\SQL2008SP3
YOURMACHINENAME\SQL2008SP3
127.0.0.1\SQL2008SP3
The exception is if the subtext has (MSSQLSERVER)
- this is a default instance rather than a named instance. In that case you would just connect to YOURMACHINENAME
or .
.
Also, no, you should not use Management Studio 2005 to manage SQL Server 2012 instances. In fact I think the above Configuration Manager won't show your 2012 instance. So before you do anything, you should uninstall the 2005 version of Management Studio, and go get the 2012 SP2 version here:
http://www.microsoft.com/en-us/download/details.aspx?id=43351
Click Download, the file you want is SQLManagementStudio_x64_ENU.exe
. The nice thing about this version in 2012 SP1 is that it's the first version of SSMS Express that is actually fully functional and license free. Previously you had to live with limitations like no SQL Server Agent management, well those restrictions are now all gone.
(When you instal the client tools, this should also give you a new version of Configuration Manager, if your previous installation of SQL Server 2012 did not provide that for some reason.)