> When I try open a Firebird database file the system shows the
> following message:
>
> "file <my-database-file> is not a valid database"
>
> The database file seems corrupted! But I can't use gfix to fix it
> because gfix shows the message above.
>
> What can I do? Any help will be appreciated.

Assuming you are of course trying to open what was a Firebird database.
What that message tells me, is that the Database Header page, the first
page in the database that effectively defines the database has a major problem
that needs to be corrected.

Paul