Iranpaak jaan;
when you pint the mouse at the link (lets assume ISP) can you see the actual URL on the bottom of your browser?
I am not sure what kind of browser you are using if IE then it is called Status Bar?
anyway if that shows you the right link but redirects you to the wrong page then what Finally said is true, well in a way....
may be you installed a new search bar like Yahoo lately?
I dont know but I hate these extra ars they fill in the space and they junk up your browser, I would uninstall them via the control panel (in Vista is called Programs something?) but in XP it is Add Remove Programs .
Also you can go to the AVG web site and get a free anti virus program or check your PC online if you think there is a virus problem. (or Avast a BT mentioned),my kids like avast better, i like avg bcs it is easier to deal with)
Anyway it may be your provider doing it too? Like in hotels or airports they do that stuff sometimes.
anyways my 2 cents. wait until the experts tell you...