1. Make sure the ethernet card is recognized and driver module is loaded on startup. can u paste the result of the following two commands:
lspci --- List all pci device
lsmod --- List loaded modules

2. If your ethernet card is not well configured, configure again using "netconfig". If you have a static IP, just give all the informations, if using DHCP, then choose dhcp.

3. After configuration, restart the networking

/etc/init.d/network restart


Good luck