Hi, you said the machine came with windows pre-installed? If it did not come with an installation DVD then it would have had a portion of the disk reserved for an image of the OS. This partition is hidden so that the user can`t accidentally delete it. Is it possible that you have used a third party disk partitioning tool?. if you have then you may have deleted the system image. If that's the case them I`m afraid you may have to purchase a new copy of Windows. Not much comfort to you now, but I`ve found Windows image files hard to work with. There are free disk imaging tools that do a much better job. You could always switch to Linux, it`s a big move, and it`s a pain sometimes to get used to new software, but some versions of Linux are aimed at Windows converts, Zorin is one that is graphically similar to windows. But best of all it`s free. So if money is an issue and you have tried everything else then it might be worth a try.
Hugh