Sometimes when you reinstall your PC, or for any other reason you need the OEM Microsoft Windows Productkey your laptop / PC came with.
Since there is no sticker with the key on the device you can use a very neat program called ‘RW Everything’ http://www.majorgeeks.com/files/details/rweverything.html
After unzipping the .zip choose rw.exe and click on ACPI.
Next go to the MSDM tab, at the bottom you will find the Windows key.