Can I use Windows 8.1 key to activate Windows 10?

Hi Nalinee. I'm Greg, an installation specialist, 9 year Windows MVP and Independent Advisor, here to help you.

When you originally Upgraded it assigned a permanent DIgital LIcense to the PC so you can reinstall WIndows 10 as often as you want, skip the Product Key during install and it will activate afterwards when it connects to the internet.

Follow the illustrated steps here for doing the best possible Clean Install which should get you past all difficulties as it has hundreds of thousands of others who have followed the steps in this link and never come back to report another problem: http://answers.microsoft.com/en-us/windows/wiki...

To create Windows 10 Installation Media (if necessary on another PC) install the Media Creation Tool and follow the directions here: http://windows.microsoft.com/en-us/windows-10/m.... Uncheck the box for Recommended Settings to choose the exact version and bit rate for the target PC only.

Insert media, boot it by powering up PC while pressing the BIOS Boot Menu Key here: https://www.sysnative.com/forums/hardware-tutor...

If the media won't boot you may need to enter BIOS/UEFI Setup (pressing key given in chart in link above) to turn off Fast Boot or Fast Startup first.

Choose the boot device as a UEFI device if offered, skip the Product Key screen and choose your licensed version only if offered. On second screen choose Install Now, then Custom Install, then at the drive selection screen delete all partitions down to Unallocated Space to get it cleanest, click Next to let it create needed partitions and start install - this makes it foolproof.

You will get and keep the best possible install to the exact extent you stick with the steps, tools and methods in the linked tutorial. It's a better install than any amount of money could buy and a great learning experience that will make you the master of your PC because you will learn everything that works best and how to apply it with your own hands.

I hope this helps. Feel free to ask back any questions and let us know how it goes. I will keep working with you until it's resolved.

If you receive a popup asking if this solved your problem please ignore it, as it may remove my ability to help you and others may also not help. Please wait until after the issue is resolved to answer the popup or mark your question answered to help others.

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Hi Nalinee, you can reinstall Windows 10 at any time and it will not cost you anything !

You should just clean install Windows 10 rather than upgrading from Windows 8.1. This will have 3 benefits, you can skip the part to enter a Product Key, if you have to reset again, it will reset to Windows 10, not 8.1 and your system will be more responsive and reliable . . .

Since you previously had Windows 10 installed and activated on that PC during the installation process skip the steps which ask for a product key and select the option 'I am Reinstalling Windows 10 on this PC', and activation will not be an issue, your PC will have a digital entitlement stored on the Microsoft Activation Servers

Make sure you install the same Edition of Windows 10 (Home, Pro . . . etc.) you previously had installed to avoid Activation issues

Click this link:
https://www.microsoft.com/en-us/software-downlo...
to download the Media Creation Tool (Click on Download Tool Now), with that you can download the latest Windows 10 ISO (Select Create Installation Media for Another PC), you can create a bootable USB flash drive (min 8GB) using that tool

Then, Boot your PC from the Installation Media you just created (change Boot Order in your BIOS) to begin installing Windows 10

If you have problems booting from a boot disc, you may have UEFI BIOS:
Insert the Bootable Installation Media, then go into your BIOS and make the following changes:
1. Disable Secure Boot
2. Enable Legacy Boot
3. If Available enable CSM
4. If Required enable USB Boot
5. Move the device with the bootable disc to the top of the boot order
6. Save BIOS changes, restart your System and it should boot from the Installation Media