If this happens, you can try this:

Click "Start" -> "Run..." Type in 'cmd' (without quotes) and hit Enter.

Then type these in hitting enter after each command:

ipconfig /release

ipconfig /renew

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If you can't renew, you can then try his to make sure that you computer is getting its IP address properly:

(If you are not comfortable with your skill level, you should get someone to help you. You don't want to cause even worse problems with your network configuration.)

1) In the Control Panel, open Network Connections, and right click on the network connection you are using, select properties

2) highlight "Internet Protocol (TCPIP)"
3) properties
4) click the button "Obtain IP address automatically"
5) Same for "Obtain DNS address automatically"
6) close all windows normally