I have had the same configuration for accessing the internet for a couple of years, when all of a sudden, for no apparent reason, it has ceased to work. I have the modem connected through a wired (dlink) router, which is then connected to my desktop and also to a wireless (buffalo) router. It stopped working and I tried everything that I could think of to revive it, with no success. When I connect my PC directly to the modem, it works fine, so there is no problem with the connection out. I am able to ping the DNS servers with no problem and the wired router is acquiring an IP address from the server. However, I cannot use either Firefox or IE to connect to the internet, nor can I use any sort of update software to get online. I have even tried disabling my ZoneAlarm software in case this was the problem, but nothing still. I have tried using both static and DHCP IPs on the network computers with no luck. I have reset the wired router to factory defaults and started over, again with no luck. Any ideas on what the problem might be or what else I could try to fix this?

What you've described doesn't point to an obvious suspect. Swapping the positioning of the two routers in the connection scheme is the next thing I would try.