What browser is that?
Something isn't right and if you haven't found it by now I'm not certain what to tell you.
Automatically detect settings is correct. Maybe it's the DNS in your router. It's possible it has been hijacked. If you have another computer check to see if they are both using the same DNS.
If you have used those other tools and none found a problem there is one more tool to try It's called Junkware Removal Tool, (JRT), and can be safely downloaded and installed here
http://www.bleepingcomputer.com/download/junkware-removal-tool/