Dr. Page Caufield:
Thank you for your post.
If you are hosting the file and cannot connect, but all clients can access, then I suspect something has changed within your computing environment.
First, uninstall and reinstall FileMaker Pro 12. Once reinstalled, run all updates so that you are using the latest version of FileMaker Pro 12. Now, launch the file and see if you encounter the same issue.
If this still fails, then make a copy of your database file and place it on the hard disk. Next, create a new user account, login to the new user account, and launch FileMaker Pro 12. Open the file on your hard disk. Does this work?
Keep me updated with any progress.
The "clover" is supposed to indicate that a script is running. This is a typical result if your script is in a long running script--possibly trapped in an infinite loop. It's the symbol for your command key and if you look carefully, I'd guess that your cursor icon shows both the symbol for the command key and the period--which is the key combination to press to abort a script if allow user aborts was not used in the script to prevent the script from being aborted.
If you have FileMaker Advanced, you might want to try launching filemaker without trying to open this file, then enabling the script debugger and then trying to open the file. If there's a script that's the culprit here, it will show in the debugger and you can click the red X button to cancel the script so that you at least have the file open without the script locking you out of the file. This method for aborting a running script works even if Allow User Abort is used to prevent the keyboard short cut from aborting the script.