Uninstall the game, and when I say uninstall, I mean:

- Uninstall it via the control panel.
- Delete the folder for the game that's in you C:\Program Files folder.
- Delete the \My Games\Final Fantasy XIV folder in your My Documents.
- Reboot
- Download CCleaner (google it) and have it run a registry scrub.
- Reboot
- Defrag your hard drive (unless it's a SSD),
- Reboot
- Reinstall FFXIV

It'll probably take you 2-3 days to do all this, but I bet it solves your problem.