Turn off your computer right now and don't run it again until you recover your product key or find that it is unrecoverable.
Remove your hard disk and take it to a data recovery specialist and just hope you haven't actually overwritten the product key stored in your old registry.
You need to know, though, that data recovery by this means, if possible, will probably cost you more than a new copy of Windows.
You probably have already discovered this; but, when you by a copy of Windows, the value is in the Product Key, not in the disk. Write the number on the disk next time.
By the way, asking for product keys here can get you kicked out of these forums.