OSX installed and have everything working so far except... Boot works if I hold F10 and select internal hard drive, but if I let it boot automatically it says “a bootable device has not been detected”

I have gone to bios and adjusted boot order and even disabled all other boot options except for my internal drive. Still gives me same error. BUT all I have to do is hold F10 at bios select my hard drive and it works great. What do? What about the boot process is different when manually selecting the drive than from when I let it boot by itself?