Did you remove all hard drives except the two for raid when installing? Otherwise it may put windows on one drive and the boot on another.
Did you put the raid drives in matching slots? both white sata III ports? Or the middle two ports (2 & 3) do not use the end black ports (4 & 5) as they are designed for optical drives.
You have two settings you need to set for hdd boot in bios.
First you need to set hdd priority BBS and have raid as first drive, then set the raid for first boot device.
You can manually boot drives with the F12 key. Don't use uefi options unless you have enabled it. If you have enabled it, then it may need different requirements for booting that I haven't used yet.
Luck
-=Mark=-