Triple boot UEFI

Hello all,

I have a computer with Windows 8.1 pre-installed (UEFI).
I installed Windows server 2012 and Kali in triple boot. All have worked perfectly until now, but after a Windows 8 update it's impossible to boot on Kali. Only the Windows boot menu is shown.
I have used the "boot repair" tool mais no change has been made.

I attach the generated boot-info report for more details (/dev/sda4 Windows 8.1 - /dev/sda6 Windows 2012 - /dev/sda7 Linux - /dev/sda8 Données)

Please help !

I had issues with my triple boot machine at one point (although the current windows update ironically messed up my win 7, not my linux distro) and found this tool helpful:

http://neosmart.net/EasyBCD/

hth