How about some more information...what are you trying to boot from? Have you installed OS X yet, or are you booting from a UniBeast installer? If you're booting from a UniBeast USB stick, is it a USB 2.0 stick in a USB 2.0 port? If not, try remaking your UniBeast installer on a USB 2.0 stick and boot from a USB 2.0 port; USB 3.0 is still problematic for this purpose.