We had to transfer the hard drive to a new machine and now I can't access it via the same IP. The local IP (which I'm trying to access it through) is static and the linux configuration hasn't changed. It's connected to the same spot on the router and all of that. ifconfig shows only lo and not eth0. Does this mean that linux isn't seeing the onboard ethernet card?
update
I can't ping www.google.com - unknown host
udev grabs the ethernet address and reserves eth* device nodes based on that address. Eth0 is "live" in the sense that your /etc/network/interfaces has brought it up, but your onboard card is probably eth1 or eth2. Do an ifconfig -a to see all (even unconfigured) devices.
Yes, if you're not seeing eth0, then there's no interface that the system is seeing. Try doing a "lspci" and see if linux can see the card, then google the card model number/chipset number, and figure out which kernel module you need. "modprobe and see if an "eth0" appears.
You may need to add the module to /etc/modules for it to be loaded on boot.
Are you running a really old version of linux? This is an error I haven't seen in quite some time.
lspci shows the ethernet card.... I'm not very familiar with modprobe, modprobe -a eth0 says "mod not found"