Check your boot sequence in your BIOS. I suspect that the PC is looking at your USB devices before your HDD. You iseally need your boot sequence to be
1. FDD - if installed
However, I have to say that, in your position, I would be inclined to only switch your USB device on when you need it - after boot-up. I cannot think of any reason, other than to boot from it, why you would have your external drive switched on when you boot up.