Alright, check this out.
SET UP A STATIC IP (If you have not. If you are not sure, do it anyways.)
PortForward.com - Free Help Setting up Your Router or Firewall
If you don't know what to choose when you input the ip, check this out.
PortForward.com Forum
OPEN THE PROPER PORTS
Determine your router (The box you connect to the internet with.) model and find it here.
PortForward.com - Free Help Setting up Your Router or Firewall
Once you find it, click the link and follow the instructions. That should everything you need.