LOOP BOOT? Here's what worked for me...

[Guest]

Try unplugging all of your USB devices. Yes, that means the extra backup
drive in the front of your PC that connects through USB as well, if you have
one. Then...it works. Amazing...

 

[Diamontina Cocktail]

Try unplugging all of your USB devices. Yes, that means the extra backup
drive in the front of your PC that connects through USB as well, if you
have
one. Then...it works. Amazing...

That is likely because your extra USB HD is set to active. Remove that and
it should be OK or alternatively go into BIOS and enforce the drive you wish
to boot from FIRST.