If you did any of that, you can continue to get Windows 10 for free on the same hardware. Select the Start catch, select Settings > Update and security > Activation , and after that select Troubleshoot. You should be marked in as a head. The troubleshooter will demonstrate a message that Windows can't be actuated on your gadget. Select I changed equipment on this gadget as of late, and after that select Next.
If you lost your product key. Just buy one key from this page:
Windows 10 Pro Product Key 32/64 Bit (Retail Version)
Here’s how you can reinstall Windows 10 if you’ve already upgraded to it before
Step 1: Download the Windows 10 installation media and install it on your computer.
Step 2: Don’t provide any Windows 10 product key during the installation process. (Just press ‘skip‘ or ‘do this later‘)
Step 3: Your Windows 10 will automatically activate after it contacts with Microsoft’s servers. It can take a while before it gets activated.