Ubuntu :: Sudden Loss Of Eth0 Connectivity

I have some boxes and laptops connected to the same lan. While messing around with xorg.conf and doing a couple of restarts, one of the boxes suddenly lost internet access.The other machines can ping each other and access the internet (the boxes through eth0 and the laptops through wlan0). That one box, however, cannot ping the others, nor the router. Both ends of the internet cable are plugged in, and there are the usual continuous green and orange lights on the box end, telling me that everything is fine with the hardware connection.ifconfig gives me:

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask: 255.0.0.0
inet6 addr: ::1/128 Scope:Host

[code]..

I have no idea what happened, since the lights indicate it is not a hardware problem. It must be a problem with that particular machine, since the others are fine. However, I have not changed any of the network config files.