hi there :wink:
you have some kind of browser hijacker. those can install themselves secretly or it might be part of some software you've installed. have you installed some search toolbar, p2p software or anything new recently? if so try to uninstall it and see if it helps.
the best way to remove a browser hijacker is to run anti-spyware, but if your browser hijacker is a part of some other software, it will come back after you remove it. if you don't use any anti-spyware yet, take a look at our recommended
anti spyware list.