Proxy error, check your internet connections

Hello,

MY Dell laptop is showing proxy error on both the browsers i.e inter explorer and firefox as well. I already checked various solutions on google and blogs but unable to solve the error. I also tried to go to options-> internet settings-> change LAN settings and unchecked the proxy server... but still my problem is not solved and browsers still showing the proxy error. I even tried using laptop in safe mode and change the settings, but the problem still remains the same. can anyone please help to get out of it.??
i will be very thankful