Have you tried booting with no floppy at all?
I was suggesting that it might have a hard drive that it boots from and having a floppy inserted can prevent that.
Those disks sound like where you would put your projects, not what you would boot from.
In fact now that I think of it, it's NOT booting from the floppy right now, otherwise you wouldn't see that "Not a DOS disk" message.
It's trying to boot from some other disk (probably a hard drive) and when it tries to access the floppy, it then tells you that it can't read it.
Having no boot disk or a bad boot disk would show a big hand on the screen holding a disk, telling you to insert one.
