A D-Link router does not need an Internet connection to act as a switch and DHCP server to support a network
1) Reset your router to the default factory configuration by holding down the reset pin for ten seconds while the router is powered up.
2) Connect all your PCs to the LAN Ethernet connectors (usually, there are four of them) on the router. Do not connect anything to the single WAN connector.
3) Ensure that all your PCs are set to automatically receive an IP address, subnet mask, default gateway, and DNS server in their TCP/IP properties settings.
4) Reboot all your PCs.
Your network should now be functional as before, with each PC receiving its IP address via DHCP from the D-Link router. All PCs will be on the same subnet and should be able to talk to each other through the built-in switch in the router.