Try these in order:
Click on start, then in search type in 'cmd' and open it. Then type this in (without quotes) "ipconfig /release" and press enter. Then wait for one minute and type in "ipconfig /renew" and press enter. Wait for another minute and then try to see if everything works. If it doesn't work then try this, disconnect the coaxial wire from your modem for one minute and reconnect it. If that doesn't work then disconnect all wires from your modem for one minute and reconnect. If this also doesn't work then press the reset button on your modem for 15 seconds and wait for a minute and see if that works. If that does not work then contact your internet service provider, it may just be that they might be having issues at the moment.