is the bios detecting the other drives when you choose your boot order?
Where is "removeable disk" or "external drive" is your boot order?
It is an issue with the board, does it happen with a USB key plugged in?
If its a UEFI bios, you havent got UEFI whatever set first?
If you just have "hard disk" as your first boot item, within that item, you need to make sure that the SSD is first.
If however, the bios isn't picking up the drives, then it could be more of a problem, since it would mean they are being detected afterward, and then inserting themselves higher up in the boot order...
If you press f8 during boot to get the boot device pop up, what order do the items show up in?
I have many systems that I manage, and have different external drives via usb 2 and 3, and the only time this happens is when the boot order is incorrect.