The issue you describe sounds like a P.O.S.T. failure. When you first start a computer whether it's a smartphone or a super computer and everything in between runs a Power On Self Test. This is the first program that every computer runs before the operating system is loaded. If there is a failure the computer will not boot. The P.O.S.T. is controlled by the BIOS. Chance are your BIOS cant' see the drive. The easy way to resolve this issue is to boot into your BIOS set-up utility and change your boot order manually.