so let's check it from the start:
1) what is your IP?
Check http://whatismyip.com and to be sure both router/modem status
Do you pay for static IP (usually paid service) or does your IP change (usually either automatically every XX hours/days or on modem/router restart) ?
Do you have Public IPv4 IP? (some ISP use private addresses with NAT or even IPv6 only with NAT64/464XLAT)
2) is D2GS running?
try
telnet 192.168.12.34 8888
(use yor PC IP instead of 192.168.12.34, to this IP should be forwarded ports on router)3) Check if port forwarding works with disabled firewall:
http://www.yougetsignal.com/tools/open-ports/