- Disable Secure boot in BIOS
- Disable fastboot and hibernation in Windows
- Try boot-repair if that is still not working
sudo add-apt-repository ppa:yannubuntu/boot-repair
sudo apt-get update
sudo apt-get install -y boot-repair && boot-repair
When i used to do boot-repair at the end of pastebin contents it has these lines
> If your computer reboots directly into Windows, try to change the boot
> order in your BIOS. If your BIOS does not allow to change the boot
> order, change the default boot entry of the Windows bootloader. For
> example you can boot into Windows, then type the following command in
> an admin command prompt: **bcdedit /set {bootmgr} path
> \EFI\ubuntu\shimx64.efi**
Try this command
bcdedit /set {bootmgr} path \EFI\ubuntu\shimx64.efi
The above command works in Windows 8 as well as 10 but this should be the last resort unless your boot-repair options gives you this option only