Windows 10: windows 10 product key not working anymore

I recently built a new PC and I'm trying to activate windows 10 but the product key isn't working.
I remove the product key from my previous computer and now even when I try to reactivate the product key on my previous PC, it doesn't work.
What could be the issue ?

:)

 

Installing Windows 10 using Windows 7 key

Nope, you need to install Windows 10 first and make sure the Windows 7 key is transferred to your Windows account after you've installed Windows 10 (not quite sure how that works). I missed the last step and I could not activate Windows 10 after a re-install... Microsoft seem to have done everything they can to make it a PITA. Also, it's technically too late to do this now anyhow, as the upgrade offer has expired. But KMSPico works quite well...

As for getting rid of Windows, delete the Windows folder.

 

Activate windows 10 after re-installing (I have lost my product key)

I own a Lenovo T430 laptop. In 2017, I installed Windows 10 using my original Windows 7 product key. Unfortunately, I cannot find that product key anymore. I need to re-install windows 10. Will it be automatically activated after the installation, if I skip the step of asking the product key during the installation?

In my opinion, I believe that my laptop will have a digital entitlement stored on the Microsoft Activation Servers and this will not be a problem. Is that true?

If not, please suggest me a solution or a workaround.

 

Finding the Windows Vista product key

Allright,I've tried the Hirens BootCD on USB drive and it works like charms.unfortunately,none of the utilities included on it helped me to recover the vista product key..but thats not important anymore,cos I just did a fresh install in the end..everything works fine,but a new issue arise.
DVD drive not recognized in my computer under Vista
tried few things but no results..what do you suggest guys?