Netzero provides a support website to help resolve common problems, look for a FAQ or support.
INHO, I think your problem lies in the "startup" of netzero. If upon orginal install you allowed netzero to startup with you bootup, and then you hit the netzero icon on desktop, you're double loading the s/w. You need only to hit the browser icon to lauch into the web. It will try to dail, etc. after hitting the broswer icon. If none of this resolves the problem, unload/delete netzero, just be sure you know your username and password. Goto the directory that netzero was on and delete *all* leftover bits. Thus, when you reload netzero again and when prompted, answer "no, for load at startup". When finished, hit the netzero icon, go through new acct., and the dail-up selection procedure setting, etc. and save them. Then connect. etc., hopefully that resolves it. That's my best guess for now. Netzero will provide phone support for a cost, should you decide that route.
good luck -----Willy