# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback
# The primary network interface
allow-hotplug eth0
iface eth0 inet dhcp
And reboot the guest
PS don't forget to fix the DNS if you can't reach a web site.
Thank you Parryg! I finally got it working by fixing network adapter settings in VBox Manager and then doing few other things on the guest as you recommended.
I think, the main problem was that I installed this VM and OS on a wireless connection at home, but then tried to run it from a wired one in the office without switching the adapter settings. Apparently, wireless did not work in the office. Once I switched the adapter selection form wireless one on a Gigabit, the things started to improve.
I did have to add primary network interfaces to the /etc/networking/interfaces too, but it did not work with "allow-hotplug" for some reason - I had to define it with "auto".
Also deleted 70-persistent-net.rules, refreshed MAC address, and rebooted - all worked after that.
Thanks again!