Littlemic I think it must be a compatibility issue between the Intel controller and Seagate external drives. My Chipset is Z97 but Gigabyte uses the Intel controller version 3.0.0.16 and it works for everything on the usb 3 except it won't start my Seagate external drive. I had the same problem with my old system which was a Z77 Intel motherboard. As I said in here before it had two usb 3 controllers - Intel for the rear ports and Renasas for the header that runs to the front ports. When plugged into the front Renasas controlled ports the drive would start every time. When plugged into the rear Intel controlled ports the drive would not start.
Jim