How do I reinstall Windows 10 pro

Download the Windows Media Tool and install.

Media Creation Tool US;  Read the instructions.   

Instructions link.

https://www.microsoft.com/en-us/software-download/windows10

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If the computer was activated there is no longer a need for a key.

If asked for a key just go to the bottom of the page and click on Skip, Do this later, or I do not have one.

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

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

Hello Mathew, 

It depends on if you would like to reset or clean install Windows 10.

If able, you could reset Windows 10 to quickly start fresh.

https://www.tenforums.com/tutorials/4130-reset-windows-10-a.html

If you wanted to do a full clean install, then:

You can use Option One in the tutorial below to create a bootable USB flash drive with the Media Creation Tool from Microsoft.

https://www.tenforums.com/tutorials/2376-create-bootable-usb-flash-drive-install-windows-10-a.html

Afterwards, you can boot from the USB to do a clean install of Windows 10.

https://www.tenforums.com/tutorials/1950-clean-install-windows-10-a.html

Hey Matthew, I'm Greg, and installation specialist in eight year Windows MVP here to help you with your new install.

Follow the illustrated Clean Install steps in this tutorial which compiles the best possible install that will stay that way as long as you stick with the tools and methods given: http://answers.microsoft.com/en-us/windows/wiki...

To create Windows 10 Installation Media on another PC install Media Creation Tool and follow the directions here: http://windows.microsoft.com/en-us/windows-10/m...

Insert media, boot it by powering up PC while pressing the BIOS Boot Menu Key: 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, then 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.

There is always a way to boot the media and install if the hardware has not gone bad, so try following the steps and if it fails report back the exact failure behavior and any verbatim error message and we will get you through it.

There is a step to rescue your files first using the booted media if you don't have them backed up: http://answers.microsoft.com/en-us/windows/wiki...

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.