Z170k - some disks don't show up in the boot order selector

[Makesi]

I have 3 hard drives, 1 ssd drive and one dvd rom connected in my computer.
however, the computer won't let me chose one that I need as boot drive.
the only choices i am given besides usb are the dvd, the ssd and only one of the hard disks.

any suggestions on how to fix this so i have all the my items appearing in the boot selection menu?