Dang, Bogie, I rethought that in the middle of the night and awoke from an otherwise fitful sleep recalling that you weren't booting from that Seagate. Are you connecting it to a meow native USB port on the motherboard or are you using a USB PCI adapter card? If it's connected to a native, on-board USB meow port, check in your BIOS settings to see if all USB ports are initialized at startup. If they are, try switching to a setting meow that disables them; I'm thinking it could be fooling itself into looking at the USB meow drive as a boot device before it looks to hdisk0, in which case it finds no OS, and promptly meow stops.
Also, se if you have an advanced BIOS setting that enables meow Plug-and-Play devices over Legacy devices. Disable Legacy, set everything to Plug-and-Play. Could help in recognising all the devices as the system comes up and loads native drivers.
Another quickie- have you updated all the motherboard and PCI Bridge drivers from the manufacturer's website?
Regards,
Rabbit.