You will have to follow these steps next: Please note that the default Windows partition (usually 'C') has to have at least 5 GB of free storage. But, you can use it to download the ISO file directly from Microsoft's servers. Obviously, you cannot install Windows 8.1 using just the product key. How Does the Windows 8.1 Product Key Help? Please note that you need a Windows PC for this task. My colleague Wayne Williams has already written a guide which details all the steps that you have to go through. If you have a Windows 8 product key, you can download the Windows 8.1 ISO file directly from Microsoft's servers, and create a bootable USB drive as well.

Windows 8.1 DVD, ISO file or product key.

Hopefully, you now have a better overview of burning a bootable USB flash drive.To create a bootable Windows 8.1 USB drive you will need the following: That'a all about how to create a bootable USB. Click the Next button to start creating the bootable USB. Select the USB flash drive option and then select the removable drive you want to use from the list. Select the correct language, architecture, and edition of Windows 10 and click the Next button. Select the Create installation media (USB flash drive, DVD, or ISO file) for another PC option and click Next. Double-click the MediaCreationToolxxxx.exe file to launch the utility. Get Windows USB/DVD Download Tool from the Official website and click 'Download tool now' under 'Create Windows 10 installation media'.

If you're planning to upgrade or install a fresh copy of Windows 10 on a system using UEFI, you can use the Media Creation Tool to create a bootable USB flash drive compatible with devices using UEFI as well as legacy BIOS. Create a Bootable USB Drive with Windows USB/DVD Download Tool

How to make a usb drive bootable