Win10 did not recognize valid Win8.1 product key after upgrade

[KJO2015]

On a Toshiba Satellite C55t-A5222 running authorized Windows 8.1, I used the Media Creation Tool to create ISO on USB; everything during install went smoothly (*with one exception); per instructions we skipped both opportunities to input a product key on the Win10 warmup lap; BUT we are getting the 0xC004C003 'invalid product key' error instead of validation. Win10 runs fine, just won't budge off the error.

*The one exception was, after we had upgraded to Win10, the laptop rebooted back to the install screen, and in my absence, my assistant installed the whole thing again. However, I used ProduKey and deduced that the correct key from the original Win8.1 was still in place.

In addition to the 0x error, we also do not have an 8.1 rollback option under Win10 Settings.

 

[Titillating]

This is because the Windows 8.1 key is completely useless, in regards to installing Windows 10. It can't be used to activate Windows 10. You seem to have skipped a couple steps in the process, probably because it was confusing as all hell.

Put it simply, what you will need to do is to perform an UPGRADE from 8.1 first. This is the only way for the 8.1 key to transfer over to 10. It uses that to verify that you have a genuine copy of Windows, then registers your device hardware to an unspecified Windows 10 key. To my knowledge, there is no way to see what your new Windows 10 key is yet. Trying to clean install without going through the upgrade process will require you to actually purchase a Windows 10 key.

After the upgrade, THEN you can perform a clean install using the ISO. NOW you can skip the product key prompts, because as soon as it is installed and you connect to the internet, it will do a check against Microsoft's records of your device's hardware setup. If it matches, it will automatically activate Windows 10 without further input from you.

In theory, you can use your Windows 8.1 key to install 8.1 on as many machines as you want, go through the upgrade process, and then be able to activate Windows 10 on it. Have not tested that myself though.


EDIT:

Rollbacks. Rollback is only available if you went through the upgrade process, and only for a month. If you went with a clean install, either via USB or ISO, it will not be available.

 

[VallleyoftheMac]

This is because the Windows 8.1 key is completely useless, in regards to installing Windows 10. It can't be used to activate Windows 10. You seem to have skipped a couple steps in the process, probably because it was confusing as all hell.

Put it simply, what you will need to do is to perform an UPGRADE from 8.1 first. This is the only way for the 8.1 key to transfer over to 10. It uses that to verify that you have a genuine copy of Windows, then registers your device hardware to an unspecified Windows 10 key. To my knowledge, there is no way to see what your new Windows 10 key is yet. Trying to clean install without going through the upgrade process will require you to actually purchase a Windows 10 key.

After the upgrade, THEN you can perform a clean install using the ISO. NOW you can skip the product key prompts, because as soon as it is installed and you connect to the internet, it will do a check against Microsoft's records of your device's hardware setup. If it matches, it will automatically activate Windows 10 without further input from you.

In theory, you can use your Windows 8.1 key to install 8.1 on as many machines as you want, go through the upgrade process, and then be able to activate Windows 10 on it. Have not tested that myself though.


EDIT:

Rollbacks. Rollback is only available if you went through the upgrade process, and only for a month. If you went with a clean install, either via USB or ISO, it will not be available.

It's a good answer. It's a shame MS did not advise of this viz Win10 ISO. Particularly no rollbacks from the ISO.