After a storm I no longer had a connection to the internet. I use a Linksys router RT31P2 for IP phone (Vonage). I also have a cable modem. I suspected the modem and the router so I changed both. I now have a D-link DI-804HV. Still no internet. I found that after changing the modem 1 of my 3 computers connect to the internet if I plug directly into the modem. The only difference I can find is the NIC. The one that connects uses a NVIDIA NForce MCP, the others use a REALTEK RTL8139/810x, the NVidia connects direct but not through the router. Connected to the router all computers can talk to each other. I tested the router at a friends and it works fine. I had my cable supplier out and they say their equipment is OK. I am not convinced. How can I determine if it is a Cable problem or in my system?

I would take both your old and new equipment to another location (maybe your friend can help you out here) that uses the same ISP. Test ALL your equipment there as if it were in your house on your network. Determine which, if any, equipment is bad. If you have good equipment left over that works, I would give the cable company a call again and inform them of your findings.