eth0 not appearing. Tried everything that seemed to work for other people

eth0 not appearing. Tried everything that seemed to work for other people

Firstly let me say I am completely new to linux so if you're going to tell
me to check something or do something, please give me a vague idea how.
Installed Ubuntu Server (newest download I could) and now struggling to
get eth0 to even be detected. The only interface being displayed is the
loopback interface, and eth0 (which should be a wired PCI ethernet card)
is nowhere to be found.
ifconfig shows only the loopback device, /etc/network/interfaces has only
these two lines in:
auto lo
iface lo inet loopback
I tried opening the file in nano (using sudo) and adding the lines
auto eth0
iface eth0 inet dhcp
but no luck. Ctrl+O should save according to the web but every time I go
back to check the file the two lines I added are gone.
Tried going to /etc/udev/rules.d/70-persistent-net.rules, however all it
says is:
# This file maintains persistent names for network interfaces.
# See udev(7) for syntax.
#
# Entries are automatically added by the 75-persistent-net-generator.rules
# file; however you are free to add your own entries.
That is all it says.
It worked fine in Windows, and I desperately need to get some actual work
done on Linux. Can anyone please shed any light on this issue? Every other
forum entry I have read has a suggested solution that works and then
everyone goes "oh great thanks" and I'm stuck here not having a clue.