Two things that spring up
a. If the website you are trying to visit has expired then its an automatic webpage redirect.
b. If not then Its either a dns / web browser hijack .
Try the following.
a. Download and try another browser .Chrome / Mozilla firefox (i prefer firefox its OS)
b. Try accessing the website from another Pc (preferably not on the same network/lan) and see if the problem occurs on the other pc.
Or you could Post the URL of the website so we try accessing it from our side and see if it brings up the same page.