I got iso from torrent (thanks to nonsense MS policy) and installed without a key with the help of the ei.cfg file . In the midst of the setup(not beginning) it asks for my poor (because MS does not deem oem key worthy of ISO access) key.
After all i entered my free MCE (which i was used on Win8) key then it downloads MCE.
Now i have Win8.1 pro MCE.
- Find proper ISO
- Use RUFUS to make bootable usb installation media from win8.1 ISO file.
ei.cfg link:
http://dosya.co/oqh210bn8w1m/ei.cfg.html
- Download ei.cfg file into "source" folder on media.