Try loading up with the game launcher, it is located in the game folder. If that works you have a number of things that could possibly be going on.
Default directory;
C:NexonMapleStory
I would get an anti-virus, clean the cpu and add MapleStory and all it's subfolders to a trusted files list. It isn't safe for a computer to not have an anti-virus. Try Comodo, works nicely for me.