I think you need to take it back to the guy and ask him to set it up correctly for you. You should also make sure that he installs a legal copy of the OS, not a pirated one. Windows comes in different versions to support different languages and it sounds like you either have a version that doesn't support Korean or else it is wrongly configured.
When you pay someone to do a job of work for you they have certain obligations to do it correctly. Take the computer back to him.