My firefox browser keep showing " proxy server not found", how to fix it?

my laptop wireless network connection works fine and can auto connect once it detects any unsecured network. From the "tools", "option", and "network connection setting" of Firefox, I configure it to "auto detect proxy server for this network". When I switch to IE browser, it has the same problem of " proxy server not found". A few months ago, I did the networking between my laptop and my house computer by myself. I wonder if it has something to do with the problem I am facing now. Please help me.....