When trying to Install Windows 8.1, you get this error:
Selected boot image did not authenticate. Press enter to continue.
Selected boot image did not authenticate occurs when Windows 8.1 tries to install, but can’t because the BIOS is set up to allow Secure Boot only. Secure Boot prevents unauthorised changes to the computer that would change the current boot process. Windows 8 install triggers this, but fails without giving the option to allow the boot sector changes.
To fix the Selected boot image did not authenticate error, restart the computer, go to the BIOS (typically hold F2 or Del key as the computer is booting up) and disable Secure Boot before retrying the install of Windows 8.1.
After Windows 8.1 installs successfully, it would be wise to enable Secure Boot again as this will protect your PC from boot sector viruses.
Addendum: If you still get Selected boot image did not authenticate when you try to install Windows 8.1 after turning off Secure Boot, you may also need to enable Legacy Boot Mode in the BIOS if your computer supports it.