Download WOLF from my site: http://www.bytemedev.com/wolf/
Run the program.
Quick trick, the key is stored in memory under the ACPI/MSDM Tables.
Now reading it is the hard part, eventually WOLF will do this for you no questions, but until it does, it requires a memory reading utility.
For this, I used RWEverything Utility.
The author has made a very nifty program.
Note: You can still be unlucky in the fact that Windows 8 uses more letters in its product keys than Windows 7. IF you are downgrading and get the invalid character message, you have to contact MS to get it activated.