OK lets try this:
1) Do you have a router?
If yes to (1) goto start->run, type "cmd" in the box and press ok. This will load a black box on the screen with something that looks like:
C:\>
At this prompt type "ipconfig"
What does it say for "Default Gateway" ? This is likely the IP address of your router.
If no to (1), you do not need to do anything else, because you don't have a NAT router.
2) Goto your web browser and type the IP address above as:
http://<Ip_address_here>
This may be something like: http://192.168.1.1/
If that doesnt work, you router may have unencrypted HTTP logins disable, in which case it is listening on different port. so try:
https://192.168.1.1/
If that doesnt work, try restoring your router back to factory settings. Get a paper clip and find the tiny button on the back of your router and hold it down for like 30s with the paper clip
then try again
If you are setting up a minecraft server, I am assuming you are trying to configure port forwarding on your router. Note that you will also need to configure your windows firewall and any software firewalls to accept incoming connections on the required ports as well.