Need Help With Error 421 In GameGuard

My friends and I were talking about B1F of the Tower of the Dead, the dungeon we entered last night in Cabal Online limited for two hours only which we managed to complete in just a few minutes. Right after I finished playing and closing the game, my computer suddenly turned off even if I haven’t shut it down yet.
I didn’t bother turning it on again because I need to sleep already. Today, when I got home from school, I tried playing again but I receive GameGuard error code “421”. Need assistance.
