"eric" <questermocolle@hotmail.com> wrote
> Hi all,
> I have an external disk with Linux, and Windows on the internal disk
> of my laptop. I have GRUB installed on the external disk, so I can
> boot either Linux or Windows. This used to work just fine.
> Lately I have been having lots of problems in loading GRUB. Most of
> the time it doesn't load and the machine just boots Windows from the
> internal disk. It seems to be getting worse with time.

The problem is unlikely to be time-related. Either the machine boots from
the external disk or it doesn't. If it does so but only intermittently, the
problem is far more likely to be cable-related than anything to do with the
contents of the MBR or the disk itself. IME of course.

> When I boot another linux on a different machine, I can read and write
> on this external disk, so the disk is not broken. I don't think it's
> a problem with the BIOS either (boot order seems fine, plus I tried
> with another laptop and got the same problem).

So you cannot boot from this disk at all? Or you can on another machine? Or
it boots intermittently on either machine?

> Questions (I've googled around but I still can't figure them out):
>
> 1. could it be a software problem with the MBR? If so, how do I fix
> it?

I guess it's not impossible. You fix it by re-installing GRUB to that MBR
(grub /dev/sdx where sdx is the external disk).

> 2. if it's a hardware problem (heads cannot read the MBR?), is it
> possible to install GRUB on a USB key and from the USB key boot
> Linux on the external disk and Windows on the internal disk?

AFAICT there is no way to do this, because when GRUB is run from the USB
key, it is only aware of the USB device, so it cannot boot a partition on
another device. This could be wrong - but I have never seen or heard of a
solution.

You could consider installing GRUB on the laptop's *internal* disk though.
It should then offer you the ability to boot from either disk, as you
choose. This would not solve the problem of why you can no longer boot
(consistently) from the external disk, but would work around it.

CC