Click Start, and then click Control Panel.
Click Network and Internet, and then click Internet Options.
In the Internet Options dialog box, click the Connections tab.
Click the LAN Settings button.
uncheck use proxy and check auto detect settings.
apply and reboot.
you should now auto connect to your isp. if it doesnt work then its likley you have some softwware running that creates a proxy that bypasses windows own settings.
find it and uninstall it as well as your ethernet driver then reboot install the ethernet driver again as this will restore windows defaults without you having to go hunting for gateway addresses and the likes.