finally found that mess was due to grub-customizer that i've had used in the past and purged everywhere; but sadly it left some modified settings behind. But thanks to boot-repair to cleanly removed that garbage and cleanly reinstalled grub 2.0 working smootly now, except that the menu still does not appear at the beginning (blackscreen for about 5 to 10 seconds, then the menu is shown)
comments about the post #135 above:
finally found that mess was due to grub-customizer that i've had used in the past and purged everywhere; but sadly it left some modified settings behind. But thanks to boot-repair to cleanly removed that garbage and cleanly reinstalled grub 2.0 working smootly now, except that the menu still does not appear at the beginning (blackscreen for about 5 to 10 seconds, then the menu is shown)