No more GRUB menu after upgrade

[Frédéric]

I have just upgraded my F29 with
dnf upgrade -y

I continued to use the system without reboot and it suddenly stopped
working. Only the mouse was working. Ctrl+Alt+FN did not work but I
was able to ssh and reboot. It took a while to close linux before
rebooting and then I did not get the usual GRUB menu where I can choos
the kernel but instead just a black screen with a blinking cursor. So
I suspect that the upgrade broke GRUB and I cannot load fedora
anymore.

I am probably able to boot with a USB stick. What should I do to go
back to normal?

Thanks,

F