System will not boot and ends up at the BIOS

I stupidly uninstalled kernel 510 and installed 515 without rebooting.
Now when I boot up, my screen goes to my bios, if I pres esc while it boots up I see the Manjaro grub screen with only the UEFI Firmware Settings option.
From a live usb (which is what I’m typing from now) I tried to install a kernel using chroot with the command: sudo mhwd-kernel -i linux515 but it could not connect to the internet, although the internet is fine on the Live USB system.

The output of: ping manjaro(dot)org from chroot

ping: www(dot)manjaro(dot)org: Temporary failure in name resolution

Ctrl+Alt+F1/2/3/4... got me nowhere.
I’m stuck now, and reinstalling would be a disaster, is there a way to fix it? Thanks.
PS: I promise that I will try to not make this mistake again and that I will not be lazy when it comes to updating my kernel.

For info you were able to remove the RUNNING kernel from Manjaro Settings Manager (or System Settings), right? Order of events, you removed running kernel and installed another one?

When you boot on the Live USB, don’t you have the “Detect Bootloader” option?

//EDIT: if you can not detect bootloader from Live USB boot menu, then you could boot on the Live USB, and chroot, and reinstall GRUB by opening a terminal, and then (instructions for UEFI, instruction for MBR behind #comments in the following):

# we chroot
manjaro-chroot -a

# we reinstal  GRUB for EFI system
grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=manjaro --recheck
# or GRUB for MBR system, where /dev/sdy is the target
# grub-install --force --target=i386-pc --recheck --boot-directory=/boot /dev/sdy

# we update GRUB
grub-mkconfig -o /boot/grub/grub.cfg

# we exit chroot to unmount the system

# we reboot

If you can detect bootloader from Live USB boot menu, then boot on your Manjaro system, and only do the grub reinstall and grub update commands with sudo

//EDIT2: also maybe the kernel installation was not successful, from chroot did you try to reinstall kernel 5.10, maybe it will use the files in package cache (don’t use sudo when in chroot, you’re already root in terminal).

mhwd-kernel -i linux510


boot on USB live manjaro
open a terminal

sudo manjaro-chroot -a
pacman -Syy ( check internet is on )
pacman -S linux515 linux515-headers
mkinitcpio -P
exit (end-chroot )