You should be opening your original post and replying there instead of putting up a new post. That way other readers, who might have a good suggestion, can scroll down through all the messages and have the full picture.
User names and account names are two different things. User names are specified in Preferences and Account names are specified when you first define the password. FileMaker confuses people a bit as the file automatically enters the user name as the default account name in the log in dialog.
It's unlikely that the password or account names are damaged. Such damage usually renders the file unusuable and you get a "file is corrupted message" when you try to open the file. It's much more likely that a change in user name during the re-install has you entering the correct password but with the wrong account name.