What should I do if the system displays an exception after Win10 adds Win8.1 key?

After I experienced Win10, I found a lot of problems. For example, when I added the function to Windows technical preview, I entered the product key of Win8.1. As a result, my system shows that my system is Windows 8.1 Professional with Media Center, 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.