As long as you don't have a record open, you should be able to get to the Manage Database dialog. Do you have a startup script that's attempting to edit the record or something? If you do, then you can use the Script Debugger (assuming you have FileMaker Advanced) to halt script execution at the beginning to keep it from attempting to edit the script.
More detail is probably needed for us to help you, though. Under exactly what circumstances are you having the issue?
You may have to force quit FM to get out of that. And that may damage your database if it is not hosted. So be prepared to go to one of your backups if the file is not hosted.
To avoid this in the future: always have a developer-only script that uses the Commit Script step with the field validation override turned on. Then you can run that script and get out of the situation without killing FileMaker...
I ended up forcing the program to quit- everything seems alright thankfully. But I was able to fix the issue and will certainly be more careful going forward.
Thanks for your help!