General

Here is the simplest/best way to do it without re-downloading it if you already have the original files.

1. When you install the new Nexon launcher, begin downloading Maplestory at default location or anywhere not in your original Maplestory folder. When it has started the process of downloading and downloaded a little, exit out of the launcher completely from the bottom right corner of windows or end the task in task manager.

2. Find the location of where you started to download/install maplestory and there should be 2 folders. Appdata and Patchdata. Copy your original Maplestory files (not folder) into the "Appdata" folder.

3. Run the nexon launcher and it will verify the files and then let you play or it will download some additional files (like 5-20 MB's) and then let you play.

Should work perfectly.

@gekkegerrit:
"Nexon Launcher" is a separate program that acts as a launching platform for all Nexon games, including maplestory.
"Game Launcher" refers to the "gamelauncher.exe" executable file that launches maplestory directly. It's a legacy file that is being phased out soon. Nexon wants us all to use "Nexon Launcher" instead.

Are there 2 Launchers ? Nexon Launcher and Game Launcher ??

@streetfights: my bad, i meant to say nexon launcher.

Also, is that where your maplestory currently lives in? Or was it created by the nexon launcher when you clicked download? Where do you normally launch maplestory from?

EDIT: I made sort of a tutorial on how to symbolically link it: https://www.youtube.com/watch?v=xxfZN9P99As
You have to delete the contents of your black cipher folder and re-verify the game in the nexon launcher after.

@masinko: did you say i should run the game through game launcher or nexon laucher I am sorry that I not good with computers. and yes I got my file like you said C:/Nexon/Library called 'maplestory'. I try again with my friend help as well and figure things out. give me more links and info thanks guys. and yes globalkorean last time took me close to 1 whole day.

The launcher itself is only a few mbytes then if you redownload the game its a 9-10gbyte file.
My original game launcher just synced with the nexon launcher, so I didnt redownload the game.

If that doesnt work then another idea is getting a better network? Any download that takes up to 24hours.. you're either living in 2008 or you're seriously over exaggerating.

You can create a symbolic link in C:/Nexon/Library called 'maplestory' that points to your current maplestory directory.
The next time you run maple via the nexon launcher, it will skip the download and go straight to verify, and after a minute or so, you can launch maple.

If that doesn't work, you can try dropping the files for maplestory into C:/Nexon/Library/maplestory.