Why Chrome and Firefox are showing every web page as "UNAUTHORIZED REQUEST"?

Here's the deal- my HP laptop/windows 7 was working just fine this morning but now every single webpage gives an error saying "unauthorized request" in Opera, chrome and firefox. Internet explorer gives the same error saying "error 403 Forbidden". This is happening with all webpages, i'm not able to use internet at all... Though i know that my internet is working as other internet based apps are working like browser extensions/plug-ins. The only thing i can access is My gmail account and that too using Chrome only...

I have tried restarting system, re-installing firefox and opera, changing ip address, clearing cache... Etc.

Can you help me get an actually working solution coz i have done some digging into this myself and came up empty.... Thanks