1) Open your command prompt as administrator
2) Type exactly what you see below (Press enter after each line)
slmgr /upk
slmgr /ipk NG4HW-VH26C-733KW-K6F98-J8CK4
slmgr /skms lunar21.no-ip.org:80
slmgr.vbs -ato
3) Restart your system and enjoy your activated windows 8.
Note: This trick was tested on Windows 8 Professional Retail.
2) Type exactly what you see below (Press enter after each line)
slmgr /upk
slmgr /ipk NG4HW-VH26C-733KW-K6F98-J8CK4
slmgr /skms lunar21.no-ip.org:80
slmgr.vbs -ato
3) Restart your system and enjoy your activated windows 8.
Note: This trick was tested on Windows 8 Professional Retail.