Who's your internet service provider? How do you connect to the internet - router or modem? What type of lead did you buy - ethernet or modem cable?
I'd suggest you unplug the network cable and make sure you re-seat both ends correctly - there should be a firm click.
Then reboot your modem or router. Switch it off, wait about ten seconds and then switch it on again. It might take between 10 and thirty seconds but your internet connection should then reset itself and you'll be able to use the internet again.