This happens for some players that had installed Windows 10 April 2018 update.
That update is known to cause many problems, not just for PKO game itself.
A recommended way to fix:
1) Navigate to `C:\Program Files` or `C:\Program Files (x86)` and 'Cut' the `Pirate King Online` folder.
2) On File Explorer navigation bar type `%AppData%` and hit enter.
3) Paste folder into `C:\Users\UserNameHere\AppData\Roaming`
4) Fix `Pirate King Online` link on the desktop to point to `C:\Users\UserNameHere\AppData\Roaming\Pirate King Online` folder in place of `C:\Program Files\Pirate King Online` (both Launcher path and working folder path)
5) Enjoy!
P.S. Someone, please make a picture guide.