Can't boot after upgrade

I upgraded to the new LTS version on my laptop and after the laptop died due to running out of battery I get:

ubuntu boot failed

screen with OK button highlighted. it does not show the GRUB screen at all. after pressing OK
I get

HDD: ubuntu boot failed

with OK button and after pressing it takes me to Windows. is this sth to do with the upgrade or my HDD is failing?
it does not even try to take me to a screen where I can run fsck.
Please, help.

This might be of some help: https://askubuntu.com/questions/111563/lost-power-during-upgrade-how-do-i-recover

Rebooting and/or losing power during an upgrade may require a re-installation.

Good luck @stephenbbb

just an update:
the problem did not arise as a result of power down during the upgrade. I was able to boot into 20.04 after the install. my daughter booted into windows once and then it was no more ubuntu.
I loaded 18.04 from a usb stick and ran boot-repair. it made me type many commands at the terminal. in the end no luck still cannot load ubuntu. this is purely a grub setup problem the hard disc is fine.