This looks like grub has dumped you to the command prompt.
I presume you see this grub prompt as well:
The most likely cause is that there is an invalid or missing grub.cfg file.
That’s the file that tells grub the entries to display on its menu - so if it’s missing, grub will give you just a command prompt.
There are two ways to solve it. The details for both differ a bit depending on whether you have EFI or not, but both depend on there being a file called grub.cfg.rpmsave, which is the file under which the upgrade saved the previous grub.cfg.
Note that quotes (as in say ‘ls’) are NOT to be typed.
The first way involves booting directly via the grub command prompt.
Type ‘ls’ and you get something like this:
(hd0) (hd0,msdos2) (hd0,msdos1)
Type ‘ls (hd0,msdos1)/’ hopefully you’ll see a listing of your /boot directory, so vmlinuz… initramfs… etc. If not, run through the other partitions ‘ls (hd0,msdos2)’, etc until you find this directory.
I’ll assume it’s (hd0,msdos1), amend the following as necessary. Now ‘ls (msdos1)/grub2’ and you should see your /boot/grub2 directory, so grub.cfg (assuming it’s invalid and not missing), grub.cfg.rpmsave, etc.
So we’ve found the grub.cfg.rpmsave and can get grub to load it and therefore show the menu that we had before the upggrade.
Now ‘configfile (hd0,msdos1)/grub2/grub.cfg.rpmsave’ and pressing enter, up will pop the menu and hopefully you can boot the PC.
Same as non-EFI except that this time the partitions will be called (hd0,gpt1) etc - rather than (hd0,msdos1) etc
And instead of searching for a directory containing vmlinuz etc, we’re searching for a partition that has an EFI directory (that’s EFI in capital letters).
Assuming ‘ls (hd0,gpt1)/’ shows the EFI directory, use ‘ls (hd0,gpt1)/EFI/fedora’ and you should find the grub.cf.rpmsave as before.
Use ‘configfile (hd0,gpt1)/EFI/fedora/grub.cfg.rpmsave’ to get the old menu.
The second way involves booting a live USB (or live CD) and finding the grub.cfg.rpmsave and copying it to grub.cfg so that grub will boot that old menu as in the first method.
Once the live USB/CD is booted, get up a terminal and log in as root (su -).
Use ‘fdisk -l’ to work out the the boot partition or EFI partition. It’s usually /dev/sda1 but it can vary.
Assuming it’s /dev/sda1,
mount /dev/sda1 /mnt
Now for non-EFI:
And for EFI:
mv grub.cfg grub.cfg.new [assuming it’s not missing - it’s probably not worth saving but to be on the safe side]
cp grub.cfg.rpmsave grub.cfg
Now you should be able to boot the machine.
PERMANENTLY SOLVING IT
Once you’re booted into the PC, you’ll need to solve the problem by regenerating the grub.cfg. You need to be root to do this.
grub2-mkconfig -o /boot/grub2/grub.cfg
grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg