Cant think why its changed Jim, unless the ports were opened only for the IP address that the PC you have no longer connected was using.
Routers are independant of the PCs that are connected to them.
You can access the router from any pc on the network by typing in the routers IP address in your browser and entering the admin username and password when prompted.
To "Tunnel Through" the NATS (routers firewall) you need to open the ports for the IP address of the PC that you want to access that program/site/service.
Different makes and types of routers call their "Tunnelling" by different names.
This can be done by either Port Forwarding, using the VPN ( Virtual Private Network) or by Adding the ports you want opening.
Hope this helps, if you are still unsure of something give me the make and model number of your router please so I can check which method yours uses.