Make sure that grub is looking at the correct location for the kernel.   I just had a situation where I copied a VM grub menu which was using LVM to a physical host on accident , when I rebooted grub errored out.   This is a work in progress..

Drop to grub command line.

esc

type ‘c’

grub>  find /boot/vmlinuz

(hd0,2)

hit esc

select your correct kernel in grub, type ‘e’

Verify your config is pointing to correct partition, if not as was the case for me, change to whatever find found and hit enter, then type ‘b’ to boot.