The master password will be specific to your files. Unless you can figure out the password, you will be unable to do much with these files.
There used to be individuals that offered a "password cracking" utility that could open such a file for FileMaker 5. I don't know if they are still available. If you can get one, you could use it to open a copy of one of your files, then go to access privileges and look for the master password.