When SQL Server is trying to open a database file at the time of startup, due to following reasons you can get an error like FCB::Open failed: Could not open a file for SQL Server.

Because before connecting to any SQL Database a SQL Startup process is initializing various database files and other data structures.
You can find SQL Server name, file name, file id, file path in the error message.

Following are the primary reasons for this error:

• Incorrect file path in startup parameters
• Maybe your anti-virus removed system data files
• Maybe problem with our SQL Server FileStream filegroup
• Someone changed the service account password
• Incorrect replacement of TempDB database
• Maybe someone deleted system data files, or its corrupted due to disk failure.
• Duplicate port issue of SQL Server instances
• Virus may affect to system data files

I just shared the major reasons of that error, because there is no any particular solution to this error. Please check all the grounds and try to resolve it.
For more details, you can access one of the Microsoft threads on this error.