If you have a license of Windows 8 or just key for it, you can easily download from the download page on the Microsoft site and perform a clean installation on a computer. However, with Windows 8.1 all on easy.
Firstly, if you try to download Windows 8.1 by entering the key from Windows 8 (it should be noted that in some cases it is not necessary to enter), you have it will not work. The solution to this problem I described here. Secondly, if you decide to perform a clean installation of Windows 8.1 on laptop or computer, Windows 8 key just will not work.
The solution to the problem I found on the English site, itself not tested (UPD: checked for Windows 8.1 Pro VSE is installed), and am therefore Windows 8.1 Standard product Key as is. Judging by the comments in the source is running. However, all described for Windows 8.1 Pro, will this work in the case of OEM versions and keys — is unknown. If someone will please post in the comments.
First of all, download the Windows 5.0 from Microsoft’s website (if you have difficulty with this, see the link that was in the second paragraph of this article) and, ideally, make a bootable USB flash drive containing the installation wizard prompts you to himself. Boot Flash easier and faster. You can all turn and with the ISO, but harder (in short: we need to unpack the ISO, to do what is described below and recreate the ISO using Windows ADK for Windows 8.1).
Once the distribution is ready, create a text file ei.cfg to read as follows:
After that, you can boot from the created installation USB drive and if you will not be asked to enter a key. That is, you can perform a clean installation of Windows 8.1 and to enter the key you will have 30 days. At the same time, after installation, activation with a product license key from Windows 8 passes. Can also be useful article deploying Windows 8.1
P.s. read that you can remove the two upper rows of ei.cfg file, if you have the professional version of the OS, in this case you can choose between different versions of Windows installed 8.1 and, respectively, for the subsequent successful activation you should choose the one that is key.