You are going to modify your hosts file, the IP address where the forums are located can and have changed.

1) Start->Run->"CMD"
2) type "nslookup forum.nexon.net"
3) goto: "C:\Windows\System32\drivers\etc\"
4) open "hosts"
5) type and save: "second IP address from number step 2 goes here" forum.nexon.net

Problems:
Q) I can't see the windows folder or some files.
A) You are a faggot, your must have hidden files and folders displayed.
Solution) In any open folder: Toos->Folder Options->view->Select "show hidden files and folders" radio button

Q) I can't open hosts
A) You are a faggot, use notepad

Q) I can't run those commands I need admin rights. I can't save the hosts file I need admin rights.
A) You are a faggot. You are using Vista with UAC turned on. Turn if off faggot.
S)Start->Programs->Accessories->Right click "Command Prompt"->Run as administrator. Do a similar thing for notepad.

Q) I literally put quotes in everything, now I fucked shit up.
A) You are a faggot.
S) Faggot.