If your machine is on a wired network (i assume it is) if you can, open a terminal and type this.
see what that prints. If it finds your network card and everything okay, in otherwords it prints information, (you'll know if it is or not) like your ip address, and subnet mask and whatnot, on one of the devices in the list, (probably going to be eth0 or eth1) than try just typing
then see if you can ping google, or test your internet connectivity however you want too.
oh, by the way, in the terminal, switch to root for the ifconfig command.