1.  Visit portforward.com, enter your router brand and model and click search.  Then read the default guide for your router.  This will show you the necessary steps to forward a port for your particular router.

2.  Download a free port listening tool (like this one).  Listen on the port you forwarded on step 1.

3.  Go to canyouseeme.org to see if it shows "success".  If you see the "success" message then Congratulations! you're done. If you see the "Error" message keep reading.

4.  Try disabling your firewall.

4a.  In Windows XP click Start, Control Panel, Network and Internet Connections, Network Connections.  Now right click on your connection (local area connection) and choose properties.  Click on the Advanced tab.  In the Windows Firewall section under the advanced tab choose settings.  Click the Off (not recommended) radio button.  Click OK, then OK again.  Now re-check canyouseeme.org.  If you still see "Error" keep reading.

4b.  In Windows 7 click start and in the search box type "windows firewall".  Click windows firewall.  On the left side click "Turn Windows Firewall on or off".  Click "Off" for both network locations (public and private).  Re-check canyouseeme.org.  If you still see "Error" keep reading.

5.  Determine if you are behind 2 routers.  This part can be a little tricky.  If you have a modem with a wireless router built-in you can skip this step.  If you have a modem connected to a wireless router then this step is for you. Also if you have more than 1 wireless router this is for you, too!

5a.  Open the command prompt (start, search "cmd", enter) and type ipconfig.  You are looking for your default gateway (if you have virtual machine software be sure you aren't looking at any of those adapters) on your ethernet adapter (wired) or Wireless LAN adapter (wireless).  It should be in the same IP range as your ipv4 address.  In my case teh default gateway was 192.168.1.1 (my ipv4 was 192.168.1.12).  Now type your default gateway into your internet browser (you should have already done this in step 1).  Find the tab or link that says status or general.  You're looking for your internet or WAN IP.  If it is in the private IP range (10.*.*.* or 192.168.*.* or 172.16.*.*) then you are behind 2 routers.  If it matches the IP shown for you when you checked canyouseeme.org then you are not behind 2 routers.  If you are not behind a 2nd router skip down to the Tips and Tricks Section.  If you are behind a 2nd router write down the IP address you just found as well as the gateway IP address and keep reading.

5b.  OK, now you know you are behind a 2nd router.  We have options here.  If you try one of these options and it still doesn't work, undo the changes you made for that option and try a different option.

	OPTION 1.  Set your 1st router in the DMZ.  Let's assume you are on DSL (whose modems are notorious for routing traffic) and your DSL modem is located at the gateway IP address you found in step 5a.  Enter the gateway IP address you wrote down in step 5a into your browser.  You should be at the control panel for your modem (similar to the control panel for your router).  If this modem is routing traffic it will have many of the same options as your router (like DHCP settings, port forwarding, firewall, etc.).  Look around for the DMZ settings.  Enter the WAN or internet IP address you wrote down in step 5a and enable DMZ.  At this point it would be a good idea to set a DHCP reservation for the IP address (or MAC address) of your router.  Somewhere in the control panel of your modem there should be options for reserving the address of a connected client.  Reserving the address of your router in your modem settings will ensure you never have to go through this step again (this would be the same as assigning a static IP to your router).  Now save your settings and re-check canyouseeme.org.  If you still see "Error" disable DMZ (leave the DHCP reservation alone) and try OPTION 2.

	OPTION 2.  If setting your modem (or 1st router) in the DMZ didn't help, it's time to try forwarding the port from the modem to the router.  Find the section in your modem's control panel for port forwarding (portforward.com might have a default guide for your modem, if not you can usually find one on the manufaturer's website).  Now forward the same port you set up in your router in step 1, only this time you will be fowarding to the IP address you reserved in the last step (the WAN or internet IP you found in step 5a).  Save your settings and re-check canyouseeme.org.  If you still see "Error" check out teh Tips and Tricks secion below.

TIPS and TRICKS (and generally just good advice)

1.  MAKE SURE you are listening on the port you are checking.  It will only show "Open" if an application on your computer is currently using it.
2.  Try a differnet port
3.  Here's a handy tool to help determine if you are behind multiple routers:  http://www.pcwintech.com/files/shanes_toolbox/detect_routers.exe
4.  Double check the IP addresses you used to set up your port-forwarding rules (this can often result in a major facepalm).
5.  If you're setting up port forwarding for your Xbox or PS3, it's a good idea to reserve their IP addresses via DHCP reservation (found in step 5b - OPTION 1).
6.  Check the firewall on both the router and the modem.  Sometimes the firewall can reject or block the port forwarding rules you just set up.  You can either create rules in the firewall to allow your port forwarding to work, or just disable the firewall (not recommended for anything other than determining if this is the cause of the problem).
7.  Did you remember to disable your software firewall (including the one that came with windows)?  Disable it to determine if this is the cause of the problem, then set up rules that allow your port forwarding to work while keeping the firewall on (there are tutorials, just ask Google for help).
8.  Make sure you don't try to forward the same port in more than 1 rule.  Some router are too dumb to perform this simple check, so remember that you can only forward a port to a single device.
9.  If you tried everything and still aren't having any luck, try turning on windows firewall, setting the rules correctly, and re-checking canyouseeme.org.
10.  Try rebooting your modem and router after you saved the new settings.  Sometimes they just need to refresh.
11.  You could try flashing your router with DD-WRT firmware.  Read here:  http://www.dd-wrt.com/site/index
12.  If you have tried everything without success, post here for help.  Maybe me or someone else knows just how to help you!