First off, I have no idea what I've done or am doing, so any help offered (which will be greatly appreciated) will have to be spelled out in great detail so I can understand what I need to do.
I've been using a computer lent to me by my friend and I was hoping to use an external hard drive I have to run Ubuntu (12.04) so I could have a more personalized space without putting his machine at any kind of risk. But now whenever I turn on the computer I get this message: "error: no such device: cb105e2b-b911-4e52-9dc6-504560332258e. grub rescue>" regardless of which OS I'm trying to load (the Ubuntu from the external HD or the Windows 7 from the internal).
I know there are plenty of questions on the same matter, but as I've stated I don't really know what I'm doing, so if I misunderstood what aspects of the answers were applicable to my situation, I could probably really mess something up, and I'd really rather not.
I don't know what details to include, sorry.