SSMS Object Explorer doesn't show any of my databases

Hi, let me go through your questions one by one.

1. Is your understanding of the three instances correct?

Yes, exactly. Each SQL Server instance is independent and manages its own databases. Your two databases are currently hosted by SQL Server 2014 (instance #1). Installing SQL Server 2025 as two separate instances (#2 and #3) did not automatically move or copy those databases.

One small clarification: "Database Snapshots" is a folder inside the "Databases" node in Object Explorer. It's perfectly normal for that folder to be empty.

2. Why do your queries always return SQL Server 2014?

Are you absolutely sure you're connecting to SQL Server instances #2 and #3, rather than connecting to instance #1 again? I have a feeling that this is a problem and I suspect there might still be some confusion about how SQL Server instance names work. When you install multiple SQL Server instances on the same computer, each instance has its own name. When connecting through SSMS, you must specify which instance you want to connect to. Especially named instances require the computer name followed by a backslash and the instance name. 

For example, imagine your computer is named MYPC and you have three SQL Server instances installed:

instance #1 => SQL Server (MSSQLSERVER) => Server name to enter in SSMS: MYPC

instance #2 => SQL Server (SQL2025) => Server name to enter in SSMS: MYPC\SQL2025

instance #3 => SQL Server (SQL2025_TEST) => Server name to enter in SSMS: MYPC\SQL2025_TEST

Since you're connecting locally, you could also use:

- . or localhost- default instance (#1) (simply dot symbol)

- .\SQL2025 - named instance (#2)

- .\SQL2025_TEST - named instance (#3)

So please open SQL Server Configuration Manager and select SQL Server Services. You should see the SQL Server Database Engine services installed on your computer. Please check their exact names and whether they're running. If not - right click and choose "Start". 

Also, while you're in SQL Server Configuration Manager, please check whether the SQL Server Browser service is running. SQL Server Browser helps SSMS discover named instances and determine which TCP ports they're using. If it's stopped, named-instance discovery or connections that rely on it may fail. You should still see all installed SQL Server services in Configuration Manager even when Browser is stopped.

Then open SSMS, select Connect > Database Engine , and enter the corresponding name in the Server name field.

There's also a second possibility worth checking. Even if you've correctly connected to instances #2 and #3 in Object Explorer, an existing Query Editor window may still be connected to instance #1. Connecting to another server in Object Explorer doesn't automatically change the connection of an already open query window.  If you look at the status bar at the bottom of your Query Editor window, it shows which server or instance that particular query window is connected to.

3. Can the same databases be attached to two running SQL Server instances?

This is an important question, and there's a distinction worth making. You cannot have two SQL Server instances simultaneously using the exact same MDF/LDF database files. However, you absolutely can have two independent copies of the same database, one running on SQL Server 2014 and another on SQL Server 2025.

For your situation, I would recommend Backup and Restore rather than Detach and Attach. Here's why:

Your original SQL Server 2014 instance is working, and you mentioned that an application depends on it. I wouldn't risk disrupting that environment just yet. Instead, you can:

1. Create a full backup of your database on SQL Server 2014

2. Connect to SQL Server 2025 (instance #2)

3. Restore the backup to that instance, making sure the restored database uses its own file locations

4. Test your queries and application against the restored database

This leaves your original database untouched and gives you a separate copy for testing

SQL Server 2025 supports migrating databases from older SQL Server versions, including SQL Server 2014. However, database compatibility and application compatibility are not necessarily the same thing. Your application may still depend on specific SQL Server features, logins, or other instance-level configuration.

Also, remember that the two copies will be independent. Changes made to one database won't automatically appear in the other.

One more important point: after restoring a database to SQL Server 2025, you cannot simply restore a new backup from that version back to SQL Server 2014. Keep your original environment and backups until you're confident the migration is successful.

4. Can you uninstall unwanted SQL Server instances through Windows Control Panel?

Yes, essentially, but SQL Server uses its own removal wizard. You can start from Windows Settings > Apps > Installed apps, find the appropriate Microsoft SQL Server installation, select Uninstall, and then use SQL Server Setup to remove a specific instance. The important part is selecting the correct instance in the removal wizard.  However, I wouldn't uninstall anything until we've confirmed which instances you're actually using and whether your application depends on them.