Can't See Anyone (Coldbird.net server playing Monster Hunter Portable 3rd)

[Haseeb]

It's definitely the NAT problem then. I am the same , I did everything , DMZ , UPNP , setting static IP etc. Basically spent 2 years to find out what the heck was wrong with my connection , why couldn't I see others. And I finally found out my ISP only provides STRICT NAT (Nat type 3).
There are 3 types of NATS (1 -Open , 2-Moderate , 3-Strict) , if you have type 3 , it means you're hopeless , it's horrible for gaming and you better go for Evolve or hamachi.
Some ISPs are like that.
But you must go to your router settings and see if you can change your nat type. Hope this helps!