I have a desktop pc with ubuntu 32bit and windows xp already installed. The installation was such that there are two hard discs, one has windows, the other has ubuntu. The disc with ubuntu had separate root, boot, and home partitions.
I installed ubuntu 64bit onto a new partition, I thought that I checked the option to use the existing /boot partition, but my new 64 bit installation (which works fine) does not use the old /boot partition, and so I can only boot windows or 64bit ubuntu.
I have installed grub-customizer, and re-run it. It shows my old grub entries, but when I try to boot them I get an error.
How do I reinstall/modify/update grub so that I can boot either ubuntu system or windows?