Can't boot Win10 from external disk?

[brutalizer]

I have an external HDD case connected via SATA cable (not eSATA cable), so I can swap 3.5" disks easily. I have installed Win10 onto several HDDs, but when I insert the disks, I cannot even see the disks in BIOS. So I cannot boot win10 from the external disks. I can only boot from my internal SSD disk. Why is that? Anyone have a clue?

 

[pendragon1]

wrong boot device or the mobo doesn't like that hdd case.

 

[northwoodsf]

Are you using uefi or legacy bios? Uefi and security boot can be difficult to work with.

On a testing system, I leave the case open and the connected internal drive on top of the case. Or use a laptop like Dell e6330 which you can easily remove and install the internal drive. It is actually fun to be able to do that.