Some shots in the dark...
1) Make sure ports are correctly forwarded. I recommend opening DMZ for the hosting computer just to check if that is the case
2) Run the game as administrator
3) Make sure you don't have the same CD-Key + Have the same version (not one original and other has some PVPGN installation)
4) When connecting to the network you have 3 options (On windows 7, not sure how it is on Windows 10) of either "Home / Work / Public" - Make sure you are both on "WORK" or both on "HOME" (I think WORK is the recommended one).
What ever happens. Make sure you are NOT on PUBLIC.
Unless that internet connection is also available to other users (like a dorm WiFi or something) Make sure its not on PUBLIC.
5) open the CMD, use the "ping" command to see if you can get a response from the other computer on the local IP.
Example.
My IP is - 192.168.1.10
My Server IP is - 192.168.1.5
From my PC I use the command - "ping 192.168.1.5"
If you get a response. That means your computers recognize each other.
If you don't, well the game is clearly not at fault as it seems like the router is blocking the connection.
Its really late and I am just putting thoughts on text. So I might be wrong on so many levels here

Dekar can probably correct me (and he will to some far more expert and detailed level).