Thank you for your post.
In the last 4-6 weeks were any other programs or fonts installed?
Does the FileMaker splash screen load or hang at a particular message?
Try pulling out all the plug-ins. Plug-ins are located in the extensions folder inside the FileMaker Pro 12 application folder. Drag any file ending with “.fmplugin” to the desktop, quit and re-launch.
If the issue persists, then try testing in a new administrator user to determine a system-wide or user specific issue.
Let me know if these steps resolve the issue or we can discuss next steps.