Do a thorough check for malware, following all of the steps at one of
these Web pages.
Help with malware:
All MS-MVP Sites.
http://aumha.org/a/parasite.htm
http://aumha.org/a/quickfix.htm
http://www.elephantboycomputers.com/page2.html#Removing_Malware
http://mvps.org/winhelp2002/unwanted.htm
http://inetexplorer.mvps.org/darnit.html
http://www.mvps.org/sramesh2k/Malware_Defence.htm
Unexplained computer behavior may be caused by deceptive software.
http://support.microsoft.com/kb/827315
So How Did I Get Infected Anyway?
For quite a few people it's by installing Messenger Plus, whose ads for
malware don't identify the malware as such and try to convince you that
you owe it to the author. See also:
http://www.wilderssecurity.com/showthread.php?t=27971
Don't ever do a "default" install of anything. Always choose Custom and
see what else is being carried along. Don't install any extras you're not
sure of.