need help on install pve again and restore data

Hi all,

we have a problem, we have remove with apt-get remove pve-kernel-... the last kernel and a engeneer have restart our server before we have installed the new kernel. how we can install the kernel again, well on his node are many vm´s. how can we backup it or install the kernel.
on boot we have only memtest?

pleas help. very thanks

regards