I recently installed the latest stable version of Manjaro Gnome on the same drive as my Windows 10 installation. I was dual booting without any problems. I have a UEFI system.
I walked away from my computer while logged into a user account overnight -- it stayed on the desktop. Upon my return, I found that the user was locked out, and when I tried to log back in through the Manjaro user selection screen, the machine froze up. I used the hard-reset button to reboot, and was greeted with a UEFI shell screen.
Not knowing what to do in the console, I pressed the hard-reset button again. This time, the machine booted straight into Windows and did not display GRUB. I rebooted multiple times, and each times it did the same thing and never showed GRUB.
At this point, I'm not even sure where to begin troubleshooting this. I logged into my BIOS/UEFI setup to look at the boot order, and it is defaulting to "Windows Boot Loader"... no other options are given for this drive. I looked over the partitions, and everything is looking the same as how it was before. Any help would be useful.