If you are planning to reinstall Windows without loosing the activation, use ABR utility.
Download the software and unpack it, then launch command prompt, switch to the program location and run activation_backup.exe
The ABR utility will create two files containing your Windows activation data, and you would really like to make backup copies of those two files to multiple storage devices.
After you reinstalled Windows, copy these two files to the ABR program folder and from command prompt run activation_restore.exe
The utility will restore Windows activation in a fully offline mode, no internet connection or Microsoft hotline required.