I have had ubuntu(currently 18.04) installed alongside windows(8.1) for over a year. I was logged into Windows when I closed the lid and after sometime when I came back, "No bootable device found, press any key to reboot" was written on the screen. After reboot, windows opened up and the grub menu didn't appear. So I tried again and it didn't show yet again.
I do not know what is causing the problem or how to deal with it? What should I do? Is my data on Ubuntu partition lost?
EDIT: Opening boot manager by pressing F12 during boot shows these 4 options under " UEFI Boot" panel:
UEFI OnBoard LAN IPv4
UEFI OnBoard LAN IPv6
Windows Boot Manager
Selecting Ubuntu option invokes the normal boot sequence and the grub menu appears. But this doesn't persists after reboot and boot directly advances to Windows. How do I make this permanent?