Well... there is a possibility that the integrated network card is not working ...
If you try to boot the computer with any other live CD and find that it is not showing in them or that it might show up in the network manager that the CD might provide but it fails to function, well, it most definitive does not work and you should disable it at the bios of said motherboard.
Just that, that's all I can think of... use a pci lan card or pci wifi for that matter!
Good luck!
If anything else, post more info.