I was on Windows 10. I installed Fedora 25 disto. My goal was to establish a dual-boot configuration. Unfortunately, I did not know anything about the difference between LEGACY (MBR) and UEFI (GPT) boot mode. So I made mistakes. After Linux installation, GRUB was installed as a LEGACY boot loader, and I lost the access to Windows 10 boot loader in UEFI boot mode.
First, I tried to fix the boot loader without reinstalling Windows 10. By editing 40_custom GRUB script, I was able to regenerate grub.cfg file to show a Windows 10 item in GRUB boot menu. But it does not work, when I selected the item I had a Windows boot manager error message mentionning c:/bcd/boot. At this time I was not aware of the fact that my Windows 10 was probably only accessible via UEFI boot mode.
So then, I booted in UEFI mode (secure boot disabled), I reinstalled Windows 10 with manual partitionning. But I still cannot reach Windows 10 neither UEFI mode nor LEGACY (GRUB is still the LEGACY boot loader). It's strange. I used diskpart tool and I saw the classical Windows partitions: System, MSR, Windows, Recovery, but also an EFI partition (formatted FAT32). I checked that my HDD uses GPT via diskpart. How can I fix UEFI booting and setup a stable Windows/Linux dual-boot? I precise that I have personnal data on a NTFS partition located near the end of my HDD and at this time I have no way to backup.
My hardware is a laptop MSI GE62 2QC Apache.