repair broken boot record

[Thomas Danckaert <post@thomasdanckaert.be>]

Hello guix-help,

my system does not boot anymore after a guix pull and system reconfigure 
(which did show a warning, see below).  It does not even enter the GRUB 
stage, I get a "Reboot and Select proper Boot device" instead.  I think 
the MBR might not have been written correctly (just a hunch, I'm no 
expert...).

During reconfigure, I did get a warning that my bootloader configuration 
used 'target', which is apparently deprecated in favor of 'targets'.  I 
wasn't paying too much attention, and ignored the warning.... I don't 
know if that could be the cause of a missing or incorrect boot record?  
(In that case, I suggest this warning should be an ERROR ;-) )

I checked using a live USB, and it seems the whole system is still there 
on the hard drive.  Is there a way to restore my system, keeping the 
existing /gnu/store?  Or do I have to reinstall from scratch, remove the 
existing /gnu/store and rebuild everything (shouldn't be too much work 
using Guix, but way less elegant :) )

Thank you!

Thomas