Have you tried (as root) #ifconfig eth0 up ?
Also, when you rebooted, did you have to wait while the system attempted to set up the network via DHCP ? If so, and it failed after several attempts (and it would have been pretty obvious) then it will just be a matter of configuring eth0 to use static IP's. (Man ifconfig
If there was no mention of attempting to start the network during boot (also, have a look through /var/log/messages et al.), then you could check to see which driver was supposed to be loaded, eg. (as root) lsmod | grep drivername .