I am encountering a problem setting up SQL Express 2012 where I need to install an instance with a specific name, "ATISQLINSTANCE" but I cannot because the "Instance name is already in use". I would like to remove the previously installed instance with this name so that I can create a new one with the same name. The existing instance does not appear in SQL Server Configuration Manager (error: MMC could not create the snap-in), and it does not appear in services. I deleted the registry folder HKEY_LOCAL_MACHINE\Software\Microsoft\Microsoft SQL Server -- thinking that this would remove the installed instance, but it still appears when I run SQL Server 2012 setup to install the new instance with the same name.
I followed the steps here https://social.msdn.microsoft.com/Forums/sqlserver/en-US/b38a8bdc-a2da-4371-a8c9-487e15e9f12a/sql-server-reinstallation-error-an-instance-with-the-same-name-is-already-installed-on-this?forum=sqlsetupandupgrade which illustrate removing an SQL Instance, removing SQL from program files, removing SQL from programs, and then removing files from the registry to delete all traces of the instance, and finally restarting the PC but the old instance still appears after these steps.
It seems that the SQL 2012 Express Setup has a step called "install setup files" and I believe there may be a reference to the old ATISQLINSTANCE in the setup files that is causing the old instance to reappear on setup despite being deleted from the registry and not appearing in services. I am not sure where these setup files are located to try to remove the lines that cause the instance to reappear on setup. The attached image shows the Instance Configuration page of the SQL Server 2012 Setup, where the problem instance can be seen under "Installed instances:".
I am at a loss for how to get rid of this instance. I need to find a way to completely remove the instance named "ATISQLINSTANCE" so that I can create a new one that is uncorrupted. I believe that SQL Express 2008 was previously installed on this machine, so this may be relevant information for someone who knows about SQL and the ways an instance can become corrupted. My company has left me on my own to fix this issue as the IT department told me they did not know how to fix this problem and chalked it up to "my machine doesn't work with SQL" I am not satisfied with this solution and I know that I can get the proper SQL instance on this machine I just need some help.