This means you have downloaded the wrong image for your RPi. If you have a RPi3 you have to choose the image for RPi2/RPi3. It seems you have used the image for RPi1 which is wrong then.

    Unlikely... I have a RPi3 and I downloaded this file:

    and when I md5sum it I get:
    ae949489a8b4d5517f65a4f842e05789 LibreELEC-RPi2.arm-7.0.2.img.gz

    which matches the link above.

    Could it be anything else??

    At the moment, the Raspberry Pi 3 box can only boot from the microSD card slot, and not from any of the USB port slots.

    So use the USB-SD Creator to format a suitable microSD card for your RPi3, and have it boot from the microSD card.

    I'm having the same issue: installed LibreELEC with USB Creator tool, no error messages, stuck at rainbow screen.

    I am booting from the microSD slot.
    Everything works great if I flash Rasbian to the same card and boot.