[Solved] Boot issue...

Hi all!
I've just installed Sierra 10.12.1 on my pc. (Gigabyte Z170 Gaming 5 - I7 6700 - GTX760)
The major problem, at the moment, is boot realated.
I can boot Mac OS only if I use the pen drive boot loader (removing in options the "nv_disable=1" parameter).
If I try to boot from the boot loader installed by Multibeast on the system disk, the OS load for a few seconds and then fail.
I'm a newbie, so...any help will be appreciated, thanks!