For the downgraded kernel you may wish to run
sudo mkinitcpio -P && sudo update-grub
As to why no other kernel (/version) works … it will be difficult to guess without some more information.
For the downgraded kernel you may wish to run
sudo mkinitcpio -P && sudo update-grub
As to why no other kernel (/version) works … it will be difficult to guess without some more information.