Did you actually wipe the drive or just reformat it?

If you just reformatted there are some recovery programs that can actually retrieve the data well enough for you to search for and find your lost license key.

Just curios...why you didn't attach the COA certificate to the computer you bought the OEM operating system for...as per agreement when you installed the operating system. Had you followed procedures then there would not be this issue going on now...would it!