updated 2021-10-26
I had windows [XP, not Vista] and an old copy of Fedora on my first of 2 hard disks and wanted to install the latest Fedora on the second one.
The first time, I did not give it permission to touch my 1st hard disk containing windoze and fedora 13, which I did not want wrecked. Problem was, the new one, on the 2nd disk, would not boot. The 2 systems on the 1st hard disk would still come up fine but the new one was not added to the boot loader menu, and I did not know enough to be able to add it to the list. I could only boot it up through the BIOS. Today, 2021, modifying the grub menu is so complicated, forget it. It is easier, safer, to just install to a blank partition on the first disk. I tried it again on an old pc and had the same result. The first disk still booted but I could only get to the second one through the BIOS. I gave up and just installed it on the first disk.
2011
I installed it letting it write to the boot-loader on the first hard disk, trusting it to not muck up my first hard disk, containing windows XP and the previous version of fedora (13), but now, nothing comes up – except the grub prompt: “grub > ” !
Clearly, there is nothing to like about this situation. It is maddening.
However, since I have a “grub > ” prompt, it occurred to me that I could give it one of the command strings, lines, that exist in the boot loader file, and get it to boot to that system, either winXP or Fedora-13. I pulled out an old backup dvd with grub.conf on it. I believe I gave it “rootnoverify (hd0,1)” and brought up windoze. It worked!
But, all that did was tell me my first hard disk and the 2 systems on it (well windoze anyway, and probably fedora) were o.k. I still had to get them in a boot loader that would work. I gave up and just installed fedora to the 1st disk . . . and I think it wiped out winXP which I decided I did not need anymore anyway.