Feeling really stupid…

Anyone running a small business network out there may know something about this; running an 8 station network 7 clients one server. Win 2000 pro for the OS on all. Using SMC NAT router for moving 4 static IPs (cable modem to WAN port on Router) to various stations for use with Terminal Services as client.
PROBLEM: Apparently, synchronization between modem and router is lost on a daily basis; I can ping out to DNS , but connot browse the net. Network maintains fine. Tried replacing the router, new cables, checked config until the cows camew home–still the same problem. Getting the runaround between the cable provider and the router folks–just no results . Any help would be greatly appreciated.