Arma 2: Operation Arrowhead | Multiplayer won't work | Tutorial

Hello guys! FrasierCraft here, and today I am helping you guys with a common problem I know a few of my friends have had.
Have you ever played DayZ, City life RPG or any other mod, just installed some files, and maybe thought that you were never going to play the vanilla multiplayer, and you actually did, but when you were to launch it, it didn't work? Well, then this Arma 2 Operation Arrowhead Multiplayer tutorial is for you! I will explain the most common reasons I know about, and I will also explain how to fix it.
If the video didn't help you in any way, I would really appriciate if you asked any further questions down below. I will promiss to do my best to help you guys out!
Thank you guys for watching, and as always, have a nice day!