Have a dlink DCM 200 cable modem. USB and ethernet. When I try to hook up a linksys router the Wan light won't go on and I get no connection. The router is fine. I had a tech friend over all morning and nearest we can figure out is that Comcast tech guy did something in the configuration of the modem. He had set up thousands of networks and has never seen this particular problem. We tried several routers, no go. Anyone have a clue or at least the IP address of the dlink dcm 200 modem so I can look at the config utility?
Turn off your computer. Unplug the router. Unplug the cable modem. Disconnect the Ethernet cables going between each of them. (Note: Make sure the cables you will use between the modem and the router, and between the router and the computer(s) are straight-through cables, and not cross-over cables.)
Power-up the modem. Wait for it to sync-up.
Connect the Ethernet cable from the modem to the router, then power-up the router. Wait for it to sync.
Connect the Ethernet cable from the router to the PC, and then boot the computer.
Check the computer's IP (in Windows, from the command prompt IPCONFIG) to make sure it's in the range specified by the router (usually 192.168.x.x by default.) If not, release the IP lease, and renew. (Note: This assumes the computer is setup for DHCP, and does not have a static IP address. If it has a static IP address, change the configuration to DHCP.)
You should now be online.
Note that it is possible that under certain conditions you can skip steps. People who say, "I didn't have to do all that!", well, more power to them. But when things don't work, go back to square one, and then go step-by-step, without skipping steps or cutting corners.
If things are still not working at this point, recheck those cables. Remember, they should be straight-through cables, not cross-over cables. If you're not sure, new cables are inexpensive.