Avoiding Slowdowns on W2K Server

We have a W2K server for a small LAN and they are currently using a cable modem for Internet access. The modem is plugged into a router, which is then plugged into the hub. When the cable goes out, the network slows down severely. Even removing the CAT5 cable from the hub and rebooting the server does not speed up the network. The server is not assigning IPs as all IPs are static (to my knowledge). What would cause the network to slowdown and how do I correct this?