Vista asking for login info when opening the browser

A friend of mine is suddenly having an odd issue where his internet isn't working and after I told him to switch his speed & duplex thinking it was the usual vista/older router disconnect issue but after that a prompt asking for login information started to pop up every time he'd open the browser or try to access the internet at all. I found a few similar cases around the web but non involved a solution. He's running a Dell copy of vista business if that helps.

Anyone have an idea about this?