I know this is far too late to help the original poster, but in case anyone wonders, the grub> prompt sounds very much like the boot drive had the GRUB multiboot loader installed on it instead of the Windows default loader. Perhaps your 2nd hard drive (the one you wiped clean to trigger the problem) had Linux installed on it at some point? If so, it’s very possible that GRUB was being used to multiboot the system, and the GRUB boot loader on your boot drive may have been looking on that 2nd drive for the saved boot information. If found, that boot info could have allowed it to boot up Windows for you automatically, which could be why you didn’t notice it until now (if someone else had removed the Linux multiboot before you got your hands on the machine).
EDIT: I just saw an even older thread of yours where you were talking about deleting your Linux partition from that same drive, so I guess there’s very little further doubt about where your problem was.
It’s too late to help you now, but depending upon which version of Windows you had, it probably would have been a fairly simple matter to let Windows overwrite your drive’s boot sector. For example, I had to do this exact same thing (with Grub, even) after I trashed my secondary Linux installation about four months ago. Getting Windows ME to rewrite the boot sector was a single DOS command and about a one second long operation, and everything was happy again thereafter.
Sorry to be bringing help so far after the fact (I only signed up on this forum a few days ago). At least I thought, since someone else might encounter this someday, it would be nicer if they came across the easier solution in this same thread.
I hope your Windows box is continuing to run happily.