Just reformat your hard drive. It's what MS advises.
http://www.freerepublic.com/focus/f-news/1609313/posts
That was only in response to certain rootkits or certain malware programs. Unless you've already remotely identified the problem as a rootkit or certain malware programs, I wouldn't haphazardly suggest this.
(I've had to deal with more than a few people who were told by XYZ hardware vendor to reformat their drives for no good reason other than to get them off the phone, without warning them that they would lose all their data and have to re-install all their software.)