Hi @Yakup Akpınar ,
Welcome to Microsoft Q&A!
Can you go to SQL Server Configuration Manager and check your instance name? Then reconnect using that instance name.
https://learn.microsoft.com/en-us/sql/relational-databases/lesson-1-connecting-to-the-database-engine?view=sql-server-ver15#to-connect-to-the-database-engine
If it's not the instance name, can you post a connection error detail, such as a screenshot of the error?
Best regards,
Seeya
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