I was able to successfully install Ubuntu 16.04.3 LTS on my HPPavilion laptop with Windows10 as the main OS. After Ubuntu installation, it asked to restart. After restart I do not get Grub menu, and it starts Windows OS. I tried disable secure boot, and lots of other things.
Note: I cannot access Ubuntu, so cannot access Terminal for commands.
I found https://www.supergrubdisk.org/ should I use this? or is there any other option?
I was facing same problem, this boot-repair software helped me. Boot-Repair is a simple tool to repair frequent boot issues you may encounter in Ubuntu like when you can't boot Ubuntu after installing Windows or another Linux distribution, or when you can't boot Windows after installing Ubuntu, or when GRUB is not displayed anymore, some upgrade breaks GRUB, etc.
Here is the link Boot-Repair