I recently installed Lubuntu 13.04 64-bit on one of my older computers (the computer is ancient - DDR1, no USB boot, yet it's 64-bit. Go figure.)
Anyway, the Wi-Fi adapter I tried to use malfunctioned very quickly, and, after a bit of troubleshooting, I gave up (for the time being.) I decided to try and get the built-in ethernet working. The Lubuntu box is wired via Ethernet to a computer running Windows XP, which is connected to Wi-Fi and is set to share it. Trouble is, Windows says the ethernet cable is unplugged, and the computer running Lubuntu is entirely oblivious to the existence of its Ethernet port.
lspci | grep -i eth returns absolutely nothing, so I can't even put the correct firmware on a USB stick and install it that way.
What's wrong? I will provide any computer/OS/BIOS/etc details requested.
UPDATE: Found out why Lubuntu wasn't recognizing the Ethernet - the BIOS had Onboard LAN disabled. I enabled it, but now the tray icon says "Ethernet - device not managed", and
sudo ifup eth0 starts spamming a bunch of stuff about DHCP, and the command never finishes.