You're not really supposed to fully reinstall Windows, you can use the "refresh my PC" thingy.
Microsoft has a completely new OEM installation type since Windows 8 that makes it a lot harder to pirate Windows. With Windows 7 all laptops of the same type shared an embedded license in the BIOS that could be validated with the right certificate file. With Windows 8 now every machine has a unique identifier.
You could try if ABR still works on Windows 8. It's a tool that backs up the license information on the software side:
http://directedge.us...kup-and-restore
It worked brilliantly in 7 and will still only work on your own laptop since the license info is linked to the BIOS, but I'm not sure if Microsoft's changes in 8 broke the tool. Could be worth a shot.