Something just occerred to me here after re-reading this thread. Im referring to the cause of the trouble in the first place. This can be a result of a worm or virus being present.
A couple of thigs to do:
Run a full online scan here
http://housecall.trendmicro.com/hous...start_corp.asp
Then Create a folder on your hard drive somewhere like in "My Documents" and name it Hijackthis
Download 'Hijack This to its own folder
http://www.merijn.org/files/hijackthis.zip
Doubleclick HijackThis.exe, and hit "Scan".
When the scan is finished, the "Scan" button will change into a "Save Log" button.
Press that, save the log, load it in Notepad, and copy its contents here.