This is some kind of Grub basic menu peculiar to the MBR installed by Debian. I have been trying to induce it on my system but couldn't. A google search for MBR 123FA yields only 2 pages -- that just shows you how rare this situation is.

All I can suggest is, when you see 123FA, try hitting "1", or "2" or "3" or "F" or "A" and see what happens.

Interesting problem -- tell us more when you learn more.