I remember you could get a trial windows in iso format direct download from microsoft, to me that was original, doesnt mean others are not hosting original windows but requires lot of research to know for sure.
With regard to your problem, its possible your hard drive is failing or you need to do a proper delete of partitions and a proper format of your hard drive then install windows 7.
Windows 7 during installation its arranged in such a way that making it appear a format is not necessary, furthermore it does a quick format unlike xp which did a full format. I use the quick format twice sometimes during install of 7 and never had an issue.