I'm assuming you are using an ethernet cable? Make sure your router is on (has flashing lights) and plugged up correctly. Make sure you are set to dynamically obtain addresses using the following steps:
Press Start > type "Network and Sharing Center" in the box and press enter > "Change adapter settings" right click on your local area connection adapter and click "properties" > click on "Internet Protocol Version 4" and click properties > make sure that your settings are "Obtain an IP address automatically" and then "Obtain DNS server address automatically".
If all that is good and you still don't have internet access, come back and give us some more details.