upgrade Jessie : plus de grub

[andre_debian@numericable.fr]

Depuis un upgrade de Jessie sur mon portable,
je ne peux plus booter, pas de menu grub.

Je dois passer par un CD Live "Super Grub Disk".
Ça marche mais impossible de ré-installer Grub,
(update-grub),
ça bloque au bout de quelques temps.

Si je lance "gparted", j'ai ces messages :

"Error informing the kernel about modifications to partition /dev/sda4 : 
Argument invalide.  
This means Linux won't know about any changes you made to /dev/sda4 
until you reboot -- so you shouldn't mount it or use it in any way before 
rebooting.

Partition(s) 4 on /dev/sda have been written, but we have been unable to 
inform the kernel of the change, probably because it/they are in use.  
As a result, the old partition(s) will remain in use.  
You should reboot now before making further changes."

La partition 4 est la partition étendue.

Merci de votre aide,

André