[ubuntu] internet suddenly stopped working

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http://ubuntuforums.org – Hi I have a laptop toshiba Z830 and its internet suddenly stopped working I have ubuntu 12.04 installed on it and it was working pretty smoothly till now. and now it has suddenly stopped working. I am able to ping wireless routers as well as other machines connected via LAN. I just tried to boot via USB and 12.04 and there internet is working so hardware wise it seems to be ok some software problem. can anybody help? Samarth (Hardware)