This may not be the right forum.
I have a new Seagate USB 3 2TB external drive. Partitioned it and installed 13.04.
When it is plugged into the USB 3 connection the drive is found by the file manager of my 'host' 12.04 system and works ok as storage but is not found by the computer when first booted up so I can't boot from it.
If I plug it into a USB 2 connection it is found and boots OK.
It seems to be pointing at some BIOS setting, maybe.
I have an ASUS M4A87TD-EVO motherboard and X6 1055t processor.