Is firewall affect internet connection?
I think there is no problem switching on /off your windows firewall. It seems the problem are:
1. Cable Configuration
Maybe your color scheme ais not sort well. or your rj 45 not inserted properly.
Check cable configuration, if you are using wired connection E.g. using UTP,STP,FTP cables.
2. Check if ure network status is not disabled. Some virus can disable ure local area network status as well as the conection to the internet.
3. If you check all those mehod try to repair your local area network by doing the following method
Start Menu\Network Place\View Network Connection then\Right click\Repair
i hope it will help you a little..