Nickname Creating Problem

HI, i have fully registered the account, and download the game, when i turn on the game, i put in my username and password, then it says i have to create a nickname, i have my nickname checked, it's valiable.but the OK key is not working, i tried to click on it multiple time, but it's still not working. i have tried reinstall the game, but it's still the same, can you help me please?