Internet Explorer ask for user&password for every web page.

Hi everybody. Everything was working fine, but suddenly i lost the internet
connection and ie ask me with a new window for a password and an user for
every web i want to access. In the bottom of ie it's said: REDIRECT.
I really don't know if it's a virus (i have installed AVG and a complete
test didn't find any virus) or any other problem.
I hope you can help me. Thank you