I am going to buy a new computer soon and I would like to sell my old one. So of course I am going to wipe the hard drive on my current computer. The problem if I have never done this before and I am wondering is there any way to wipe the hard drive but keeping Windows 7 OS on it and for it to be completely functional still for whoever buys my PC? If there is a way to do this I would prefer it to be free and please leave a link or something on what I need to download/do in order to do this if its possible. Thanks.