[ubuntu] no network connection after changing provider

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http://ubuntuforums.org – pls help I have a PC with WIN7 and Ubuntu10.04, using Grub, it is connected thru a modem+switch. There are 2 other PC connected thru the swich, all able to surf using Win and Ubuntu. The problem with this particular PC is that it doesn't recognize the connection (Network Manager (N-M) has a red !). The Win OS did connect. I edited the /etc/network/interfaces file which is shown below by adding the last 2 lines auto lo iface lo inet loopback auto eth0 iface eth0 inet dhcp saved it, restarted, Nothing changed I then did R-click on the N-M icon, it shows Networking and Notifications as checked E (Hardware)