However, I find the other part of your comment non-constructive. If you don't think that my question is inappropriate for HN, fine. But just writing it off without giving any justification or advice doesn't do anything to improve the community.
I normally use a Linux boot disk to boot in live CD and then I format my disk and use an utility that writes random bits on the drive. I can't remember how this utility is called but I think a quick google search will give a lot of results.
By the way, this isn't really an appropriate question for HN.