strange grub (or yast) failure on ide + sata compaq dc7100 sff

I use a lot of hp/compaq dc 7100 computers (These computers are second hand hardware I reconfigure for giving them for free). I already had a small problem with the boot (need to boot in failsafe mode - reported in bugzilla), but probably with no relation to the one I dicuss here.
On one computer I keep for experiments, I changed the original sata drive for a much bigger one (500Gb). I also added an IDE drive (120Go Maxtor).
The maxtor drive have a working XP install.
The 500Gb sata drive have a working 11.4 install.
However, since I installed XP on the other drive, I can’t make the computer boot openSUSE!
When I have the boot order IDE then SATA, XP boots as installed (no grub menu). When I use sata then ide, I have a “no operating system” error.
I can run the rescue system from a dvd, mount the opensuse partition (primary sdb3) on /mnt --bind sys, dev and proc, and then run yast and configure the boot loader from there, but when I reboot I have the same thing, no change visible. grub-install is deprecated.
any idea??

Try using:
updategrub for openSUSE Legacy Grub (not update-grub!)

the forum login is buggy, it doo not return to the original page and eat my answer :frowning: here it again

it’s nearly impossible to install updategrub from the rescue system

I removed the IDE hard drive, but YaST could not either install grub (still “no operation system” error). I guess it’s the rescue system chroot thet disturbs.
I giveup and reinstall from scratch