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'F8' doesn't work for Win8/8.1 systems, so try holding the 'shift' key as you restart Windows to enter 'advanced startup' mode.
If you have everything backed up and want to erase you hard drive, just choose to 'Reset your PC' in the next menu that pops up.
Look under 'Advanced options' if you prefer to change the Startup Settings and enter Safe Mode instead.
Hope this helps and not sure about removing the ROG boot image, so hopefully others have some good ideas, but look under 'Advanced options' for the UEFI Firmware (bios) Settings if you want to see if there is a way to do this in the bios settings.