GNU GRUB, Minimal BASH-like line editing screen displays before the usual GRUB screen when dual-booting Ubuntu 14 and Windows 8.1
Solution 1:
You've got two GRUB instances; one of the (boots first) is broken, the other one is OK.
Two possible scenarios.
- Each of HDDs has GRUB installed. System firmware trying to boot from one HDD (order usually defined by firmware settings), but it's GRUB installation is broken (you got just GRUB shell). After you exiting (typing
exit) this GRUB instance, firmware gets control back and try to boot from another HDD, which has working GRUB installation (boot menu shown). - (Less probable) Both GRUB instances located at one HDD: one is started from "EFI System partition", the other one - from "BIOS boot partition".
Common solution is to set firmware to start boot from the other GRUB (or HDD depending on your firmware settings). (In case you need more detailed steps to change boot order, please describe how your system firmware boot order settings look like.)
As a supplement, I'd recommend to cleanup removing broken GRUB instance and make sure that working GRUB is located at HDD with Ubuntu. (In case you need more detailed steps, please post each HDD partition table.)