Major Geeks says to do this first (http://forums.majorgeeks.com/showthread.php?t=35407) to eliminate malware. If that doesn't fix things, here's their how-to (http://forums.majorgeeks.com/showthread.php?t=74216) for HiJackThis (if memory serves, it downloads directly from MajorGeeks). It's a pretty long-winded set of instructions; you have been warned!