I've got a lovely installation of Ubuntu 12.10 running on my Lenovo i5 mostly swimmingly and have been enjoying it without complaint for the last month or so. This machine initially came with a Windows install that I turned into a Linux Mint install, before deciding to go Ubuntu for my main Linux needs and computing pleasure. I purchased a new, larger-capacity HD for that purpose, swapped it into place and got Ubuntu up and running (with a few issues a long the way, as evinced by my previous postings in this most heplful and amicable forum - thank you for reading, as always).
It has come to my attention that I need to boot into Windows for something, so I dusted off the formerly internal HD that now lives in an external and shares its disk with the Linux Mint install and the Windows 8 install. I recall these things working just fine in the past; I tested everything and was able to get into all OSes at will in various swaps and configurations. So I didn't expect to encounter any trouble at all after all this time. Of course, that was naive, at best.
I plugged in the external, hit the BIOS to select the disk and got an error immediately upon boot, the famed GRUB REPAIR> .
So, what's my best course of action here? Do I need to reinstall grub from my Ubuntu install, the primary (only) OS on this machine's internal HD? Do I need to do something with this external? Is the issue that I need to invoke grub from the Ubuntu disk and by selecing to boot off the external in the BIOS I bypassed that process?
Looking for ideas. I've not messed around under the hood in over a month and I feel like I'm fuzzy on what I had going on before. Thanks so much.