I think you have to "link" again proxmox with it's lvm storage, but then you will not have the <VNID>.conf files that tell proxmox how VM are formed, name of virtual disks and so on. You could try to recreate manually with an editor, maybe taking inspiration from a different proxmox server where you can create "dummy" VM as much like your memory permits you as your old ones.
Or, if you have backup of them, try to untar the dump and extract the .conf (as far as I've tested, is named qemu-server.conf, you have to rename with <VMID>.conf and put in the proper position, that is for 2.1 /etc/pve/qemu-server/, so you will have i.e. /etc/pve/qemu-server/101.conf).