Grub boot issue

I don't know if this is the right place, but i thought it would be... i do not have any problem installing Kali and grub. I do all the installation process.
On my machine, i have windows 8.1 installed already, It boots fine. Then, i create a new partition on the same hard drive that my windows is installed. I do the installation process without a problem. Then, i am able to dual boot fine. When i start my computer, the grub menu appears and i have the choice of booting to Kali or booting to windows boot manager. I tried booting windows, it works without any issues. Then i restart my computer, boot into kali, everything is OK.

I install the updates on Kali, do my stuff. It works fine for 2 days. Yesterday, i went to school, started my laptop, grub was fine, i booted into windows, listened to my online class. Then, i had another class, just put my laptop on standby, went to my other class. Last night, when I got home, i wanted to go on my kali partition. When i started my computer, Grub was not there anymore. Instead, i'd go straight to windows boot manager. No more grub.

I did not do any updates, i did not install anything, i didn't change any setting in my bios. ( I have an MSI GS60 ghost pro)

i tried fixing grub many ways, including booting a live session from USB and mounting my partition (mount .../sdb6(in my case) mount /dev /mnt/dev etc...) this didn't work either.

I can't find a way to add Kali to the windows boot manager... and there doesn't seem to be a way.

My windows 8 installation was done in UEFI so was my Kali partition.
I don't know where GRUB is, and nothing i do seem to be able to fix it. (I also tried installing grub to the boot partition, and even on my second hard drive)

Has anyone encountered this issue.