There are few things you can try.

Try in order:
1. remove the "read only" flag for the following folder, when asked do it recursively: C:\Users\{pc user}\Documents\My Games\FINAL FANTASY XIV - A Realm Reborn
2. remove the "read only" flag for the following folder, when asked do it recursively: C:\Program Files (x86)\SquareEnix\FINAL FANTASY XIV - A Realm Reborn
3. rename the following file (prepending _ for example), this will reset your launcher settings: C:\Users\{pc user}\Documents\My Games\FINAL FANTASY XIV - A Realm Reborn\FFXIV_BOOT.cfg
4. rename the following file (prepending _ for example), this will reset your game settings: C:\Users\{pc user}\Documents\My Games\FINAL FANTASY XIV - A Realm Reborn\FFXIV.cfg
5. rename the following folder/s (prepending _ for example), this will reset your character settings/widgets: C:\Users\{pc user}\Documents\My Games\FINAL FANTASY XIV - A Realm Reborn\FFXIV_CHR{16HEX}