I have a computer that I am going to retire and probably sell it at a flea market. It originally came with Windows XP but windows 7 has been installed. I really don't have any important info on the computer but still don't want someone to access it. Can I do a restore to original settings? And if so, will it have XP reloaded on it or Windows 7. I don't have a Windows 7 disc or a license COA # to put on it. I really don't want to remove the hard drive as it would not be worth a new HD. And if not what files do I need to remove?