This is JaeHwi from KoreanClass101.com
Could you check if you can see the small blue box on the right bottom of the screen? If you click the box, you can see the keyboard types such s EN or KO (For Korean) Although you installed Korean IME, sometimes the default can be changed to English setting. In that case, you cannot switch languages although you press right alt key. So please make sure if you can see 'KO' icon on the little box. If not, please select KO instead of EN on the box so that you can type Korean and also switch languages.
If this doesn't work, I think you can also get some answers by searching 'Change default language setting IME' on search engine.
I hope this helps.
JaeHwi / KoreanClass101.com