[kali 2.0] installing issue

Greetings !!

I'm the animator of a classroom where each student has to install a linux distribution, one of my student decided to install Kali in dualboot with windows 8 as first OS.

I installed thousands of linux distribs for dual boot in my life and it's the first time I feel so confused.

Facts:

The system is working but there is no way to boot on windows 8: there is a program that checks for disk integrity that is launched (I first thought it was normal as we created new partitions (/ and /swap) from the free space from another partition)
Kali 2.0 boots normally.

Analysis:

It seems that (and I always ask myself how we did it) the bootable Windows partition has been corrupted.
Attachment 946

Above, you have the sreenshot the student did.
During the set up we created the root partition and the swap partition from a "free space" that was displayed without any other information.

Nothing was said concerning spawning or shrinking of another partition. I also be focused on formatting the right partitions (the F letter was set for each partition to be formatted: sda4 and sda7)
In my mind and experience, each time I installed a Linux over Windows I NEVER lost one bit of data on Windows partitions.

Questions:

As (and I didn't know that, as my student never told me about) the Windows partitions were set in GPT. Is that change something ?
I used gdisk instead of fdisk to know why there was missing at least 400Go of data at first check with "fdisk -l".

My student can not estimate the amount of data stored in the Windows partition before the kali installation.

Is that possible to merge the free space with the partition set to be booted in grub2 (using gparted) ?

I asked the student to send me the copy of the /boot/grub2/grub.cfg file. Waiting.

I am thinking that your student made a first mistake when he/she prepare free space for Kali (any Linux).
First shrinking of partition when is Windows installed first you should do always with diskmgmt.msc from Windows.
In that case you don't need any tool to format any partition, because the Linux will do it in process of installation, except in some special Linux distro like Slackware..
try to repair to boot windows (if it possible) with Hiren's boot or boot repair cd
http://sourceforge.net/projects/boot-repair-cd/
or if is not possible then try with some boot repair tools to recover just data from computer.

Thank you, I realized, reading how to install Kali that lot of steps have not been correctly checked, the student told me that he followed the steps but couldn't boot from his usb key.

I suppose using "testdisk" to retreive data wouldn't be efficient as the entire partition has been unallocated and lot of "movements" have been operated on the hard disk during the install of Kali.