It's like rockinn said, NAT problem ...
It's really complicated for a lot of people ...
The best would to try the old server files in order to knows if they supports NAT mode protocol.
In routers it's really pain in the *** to get them in bridged ...
I tried even DMZ in order to open all ports directly on the computer but it doesn't works ... this server is not secure at all ... at least ipcop on another machine could filter all packets with snort but it's not the problem here ... it's ROUTER ...
Edit: No-IP won't work because its redirects only to the ip but doesn't pass the NAT ...

Edit: But in DMZ mode, all ports are open and listens on the specific computer, and still if i do that it doesn't works ... I don't know if it's really NAT or something other who make fail :/