Others can't connect to my private server

[Bloderz]

Hai there, Today I've been setting up my own private server in order to do a series of lets play with this mod with a couple of personal friends.
My computer is running it just fine and I've port forwarded (I think i have at least, I've done it from mostly memory) And I can connect and such by using Localhost in the address bar.
But when i give the correct connecting IP to my friends that will be helping me, They say that the server isn't reachable,
I don't know what I've done wrong! >.<
Also when i try to run the server again after stopping it correctly, It tells me that another server is running on the port, The only way I've been able to fix it is to delete the file ForgeModLoader-server-0.
I was also wondering if this is right or not.
I've pretty much been trying to figure it out myself, and it is honestly driving me crazy now, All my friends have gone to bed and I really want to get this up by tomorrow day time so we can all make a start.

Thank you for reading, and i'm sorry for my nubness >.<
Bloderz,

 

[Greedseed]

Check your port if they are open or not threw this website.
http://canyouseeme.org/

Also look at Router and PC firewall !

 

[Bloderz]

Check your port if they are open or not threw this website.
http://canyouseeme.org/

Also look at Router and PC firewall !

Appareantly it's not open, How to open it? *Sorry i'm completely new to this kind of thing i guess*

Also I've ran a server from my computer before, be it a Vanilla/Bukkit server, and people have been able to connect, Surely that means my Router and PC firewalls are correct? Or must i do something different for the mod pack?
I'm sorry I'm quite the dull person so it's sometimes harder for me to understand things,
>.<
Thank you very much for your help,
Bloderz,