Grub does not load after bios update

I have encountered a similar problem. This worked for me.

1. Log-in to Windows using your Administrative account.
   Right click on windows icon and select command prompt(admin).
   Run this from the command prompt:
   bcdedit /set {bootmgr} path \EFI\ubuntu\grubx64.efi
   This will make Grub the default boot manager. Then in the Grub menu, you will find both Windows and Ubuntu.
2. If in the Grub menu you could not find Windows bootloader then, select the advanced option (which is just below Ubuntu) in Grub menu. Then select Ubuntu(Recovery Mode). There you will find update grub. Select it and press enter. It will fix the problem and then in Grub menu there will be Windows boot loader.
   http://myviewsonfoss.blogspot.in/2018/05/how-to-fix-grub.html

This happens because on updating BIOS, its preferences and settings changes to default i.e. mode gets set to Legacy mode instead of UEFI mode, also the order of UEFI is reset to put windows first and ubuntu later so just switching mode won't work, you will also have to change order. Follow these steps(f1 or f2 keys may differ on different laptops)

1. Restart System and enter BIOS (using f2 key or other)
2. Change the mode from Legacy to UEFI
3. Change the order of UEFI to put Ubuntu on top, atop Windows. This will ensure that grub menu is loaded on startup.