Go to the following folder:

Documents\My Games\FINAL FANTASY XIV - A Realm Reborn

Inside there you'll see some FFXIV_CHR folders (one for each character). They contain your gearsets and hotbar settings. Try moving those files somewhere else and then logging back in (the game will create them again automatically).

If it works then the files were corrupted, if not just move them back and unfortunately wait for someone else to think of another solution.