There is one way to recover the "lost"CD key via load hive using regedit, please be cautious with what the mouse click when working with regedit, any unintentional double click on any file with .reg will result in force add/update of the corresponding registry key regardless of whether or not you want it to be.
Remove the HDD from the laptop and connect it to a working desktop machine, bootup the machine as usual. When you are in the desktop, go to start>run then type
regedit, right click on the
regedit (at the top of the searched result) then select "runs as administrator".
In the registry console, click Load Hive then point it to the laptop's HDD %system% a.k.a. C:\Windows. Run
Keyfinder to retrieve the "lost" key.