You unplug the gateway, which is your modem that you have to get Internet.

Did you also turn off the Gateway to flush the IP tables and any old information that it could be retaining from when the computer had the previous OS.

If you are running any kind of third party...

If you did an upgrade, there are issues when the upgrade moves stuff over from the old OS folder to the new one. Only way to fix is do a Clean Install. That means downloading and burning either to...