how to enable this again in the server?
tcp / ip filtering is al off so this means it's configured into the router or can you config it locally on the pc somewhere?

i am not sure but on my router i have u set this locally up because my router have the same problem (hardwarefirewall) so u have to enbale ports over 1000 !

does your port 21 works fine?

- need a port forwarding for the pasv-mode range on the router
- setup those port in your ftp server

for dynamic IP-->
in serv-u, click on your domain server, enable "dynamic dns" and press f5 in the opened mitre

All should be nice