I don't think we have enough information to tell you if your eth0 has failed. We don't even have the device model or any other newtwork hardware info, although I doubt that the model number would help in this case. My first approach would be to cycle power on both the computer and router, although it could even be something as simple as someone unplugging the network cable. Does this system also have Windows on it? Does that get a DHCP setup?

You can bypass DHCP by running netcardconfig and answering the first question about DHCP in the negative.