If you want to install or reinstall Windows 8.1 and don’t have installation media, you can create it from this page. You’ll need to use a PC with a reliable Internet connection and either save the installation files to a USB flash drive or burn an ISO file to a DVD.
To install Windows 8.1, do one of the following:
Connect the USB flash drive to the PC where you want to install Windows 8.1, browse to it in File Explorer, and then open the setup.exe file. Follow the instructions in setup.
Insert the DVD into your PC, and then restart (reboot) it. Follow the instructions in setup.