Win10 system increases the problem caused by Win8 key

Experience Win10 can find many problems, such as entering the product key of Win8.1 when adding functions to Windows technical preview, the result shows my system in my computer system Media Center is included for Windows 8.1 Professional and the display is not activated. What should I do?
Workaround
It is not recommended to use the previous product key to add to the Windows 10 Technical Preview, as this may prevent you from getting updates for the Windows 10 Technical Preview.
To ensure an update to the Windows 10 Technical Preview, it is recommended that you re-download the ISO file and reinstall the Windows 10 Technical Preview.
System Home has also explained the key mechanism of Microsoft Windows system. Basically, a system key can only be used in this system. Even if it can be updated freely, it is not activated by the old key on the new system. Instead, upgrade the old system.