try ifconfig as root in a terminal
you should see something like this
eth0 Link encap:Ethernet HWaddr 00:16:36:9A:C0:72
inet addr:xx.xx.xxx.xx Bcast:xx.xx.xxx.255 Mask:255.255.255.0
UP BROADCAST NOTRAILERS RUNNING MULTICAST MTU:1500 Metric:1
RX packets:666 errors:0 dropped:0 overruns:0 frame:0
TX packets:744 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:458381 (447.6 KiB) TX bytes:133674 (130.5 KiB)
Interrupt:16
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
if All you see is the "lo" section then you try bringing up the interface like this
ifconfig eth0 up
if there is only one ethernet port on your box, this should work... otherwise, if this does not work, try eth1
On whichever interface the command works, you'll have to get an IP address, so if you get no error on eth0 then do
dhcpcd eth0
or eth1... depending on which one worked...
That is assuming you use dhcp... if you use static ips, then I can't help you there... maybe someone else
HTH