Download and run Hijack This! it will find the hijacker and delete it for
you. Make sure your anti-virus software is up to date and that you have
also updated your firewall software.
Note that AdAware and SpyBot S & D will each catch some things the other
won't. Also, each need to be updated before every use, even when just
downloaded. There's also a lot more to do than just those two programs.
If trying everything at that site does not fix the problem please post back
in the same thread.