Try going into your BIOS and see if the hard disk is listed as a device in your computer.
My GUESS is that your internal computer BIOS has "lost" the fact it has a hard disk inside and it may just be a case of going into the BIOS and allowing it to "find" it again.
If you have never been in your BIOS then let us know and we will tell you how to do it.
As you have discovered, it is a good idea to back up an image of your hard disk, maybe to a second hard disk, before making these sorts of changes.
That way, if the hard disk, or the Windows image, gets damaged at least you can recover quickly.