Clean install of windows 8 will not accept your upgrade license key
If you try to perform a clean install you may run into problems. If you enter your upgrade key during install it may tell say you have an invalid product key. If you wait to enter your key after installation in the GUI it will tell you that upgrade key cannot be used for a clean install. Here is a workaround.
Open up Command Prompt with Admin (windows key x)
type in the following command
REG ADD HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Setup\OOBE /v MediaBootInstall /t reg_dword /f /d 0
then type in
slmgr /rearm
then reboot
you should now be able to enter your upgrade license key
Happy Windows 8
Cheers
Rescue PC